Brain Health: The Complete Guide

Key numbers at a glance

How your brain works and how it changes with age

Your brain is made of billions of nerve cells, or neurons, that communicate through electrical signals and chemical messengers across connections called synapses. Different regions specialize in movement, sensation, language, vision, memory, emotion and planning, but almost everything you do relies on many regions working together. The brain is also hungry: although it is a small part of your body weight, it uses a large share of your energy and depends on a constant supply of blood carrying oxygen and glucose. Even a few minutes without blood flow can cause lasting damage, which is why stroke is so serious.

The brain is not fixed. Throughout life it forms new connections and strengthens the ones you use, a property called plasticity. This is how you learn a language, recover some function after an injury, or adapt to a hearing aid. Researchers also talk about cognitive reserve: a brain with rich networks, built over a lifetime of education, complex work, social contact and new challenges, seems better able to keep working well despite age-related changes or disease.

Some changes are a normal part of aging. Many older adults take a little longer to learn new things, find it harder to multitask, and occasionally struggle to retrieve a name or word that comes back later. Vocabulary, knowledge and judgment often hold steady or improve. What is not a normal part of aging is memory loss that disrupts daily life, getting lost in familiar places, or a change in personality. Those changes deserve a medical checkup, and many of their causes are treatable.

Memory problems: what is normal and what needs checking

Forgetting where you left your keys, or walking into a room and wondering why, happens to everyone. The difference that matters is whether memory and thinking problems are getting in the way of everyday life. Signs worth a checkup include asking the same questions repeatedly, struggling to follow a conversation or a recipe that used to be easy, losing track of bills or medicines, getting lost on familiar routes, poor judgment with money, withdrawing from activities, and changes in mood or personality that family members notice.

Memory problems have many causes, and several are treatable. Depression and anxiety can affect concentration and recall. Thyroid problems, vitamin B12 deficiency, poor sleep, sleep apnea, heavy drinking, and side effects of medicines, including some sleep aids, allergy medicines and bladder medicines, can all cloud thinking. Hearing and vision loss make it harder to take information in. That is why memory problems should be checked rather than assumed to be dementia, and why the first steps are usually a full history, a review of medicines, blood tests and a short memory and thinking assessment.

Bring someone who knows you well to the appointment, because they may notice things you do not. Bring a list of all your medicines, including over-the-counter products and supplements, and be honest about alcohol and sleep. Avoiding a checkup out of fear of the answer is understandable but costly: if the cause is reversible, you lose time to treat it, and if it is not, an early diagnosis gives you more choice over treatment and planning.

Mild cognitive impairment

Mild cognitive impairment, often called MCI, means memory or thinking problems that are greater than expected for your age and can be measured on testing, but do not stop you managing daily life independently. Some people with MCI go on to develop dementia, some stay stable, and some improve, particularly when there is a treatable cause. A diagnosis of MCI is a reason for regular follow-up, a careful look at risk factors such as blood pressure, hearing and sleep, and a conversation about what to watch for.

Sudden confusion is different

Confusion that comes on over hours or days is usually not dementia. It is more often delirium, a sudden disturbance in attention and thinking caused by infection, dehydration, a new medicine, surgery, pain or alcohol withdrawal. Delirium is common in older adults in the hospital and can be the first sign of an illness such as a urinary or chest infection. It needs urgent medical care the same day, and it often improves once the cause is treated. Call 911 if confusion comes with weakness, trouble speaking, a severe headache, fever with a stiff neck, or a head injury.

Dementia and Alzheimer's disease

Dementia is not a single disease but a term for a decline in memory, thinking and reasoning severe enough to interfere with daily life. Alzheimer's disease is the most common cause. Others include vascular dementia, caused by reduced blood flow and small strokes in the brain, dementia with Lewy bodies, which can cause visual hallucinations, movement problems and big swings in alertness, and frontotemporal dementia, which often starts with changes in behavior or language and can begin at a younger age. Many people have more than one type.

Diagnosis usually involves a detailed history from the person and someone close to them, memory and thinking tests, blood tests to rule out other causes, and often brain imaging. Specialist tests, such as PET scans, spinal fluid tests or newer blood tests, can show the protein changes of Alzheimer's disease and are used particularly when deciding about newer treatments. A diagnosis can be hard to hear, but it opens the way to treatment, support, safety planning and decisions made while the person can still take part fully.

Treatment depends on the type and stage. Some medicines can ease symptoms of memory and thinking for a time in some people. Newer anti-amyloid drugs, lecanemab (Leqembi) and donanemab (Kisunla), are FDA-approved for people with mild cognitive impairment or mild dementia due to Alzheimer's disease who have confirmed amyloid in the brain. They are given as regular infusions or injections, modestly slow decline rather than stopping or reversing it, and carry a risk of brain swelling or bleeding that requires regular MRI monitoring. Whether they are right for someone is a detailed conversation with a specialist.

Living well and planning ahead

Much of good dementia care is not about medicine. Staying physically active, socially connected and engaged in meaningful activity, keeping hearing and vision corrected, treating depression, and managing other health conditions all help people function better for longer. Practical steps such as simplifying routines, using calendars and pill organizers, and making the home safer reduce daily stress. It is wise to put advance directives, a health care power of attorney and financial arrangements in place early, while the person can make their own choices. Family caregivers carry a heavy load, and caregiver support, respite care and education make a real difference to both of you.

What you can change: risk factors and daily habits

No one can guarantee they will avoid dementia or stroke, and age and genes play a large part. But research links a meaningful share of dementia risk to factors that can be changed, many of them in midlife, and the same factors drive stroke risk. The encouraging message is that what is good for your heart is good for your brain. The brain depends on healthy blood vessels, so anything that damages vessels, such as high blood pressure, diabetes, smoking and high cholesterol, also harms the brain over time.

Blood pressure is a key target. Normal blood pressure is under 120/80 mm Hg, and high blood pressure begins at 130/80. Because high blood pressure usually causes no symptoms, the only way to know your numbers is to have them checked, at a pharmacy, a doctor's office or with a validated home monitor. Treating high blood pressure lowers the risk of stroke and is linked to better brain health later in life. Managing blood sugar if you have diabetes, and cholesterol, matters for the same reason.

Hearing

Untreated hearing loss is linked to a higher risk of dementia, as well as to social isolation and low mood. One likely reason is that a brain straining to decode sound has fewer resources for memory and thinking, and people with hearing loss tend to withdraw from conversation. Many people wait years before doing anything about it. Get a hearing test if you or others notice you are missing things, and wear hearing aids consistently once you have them. Over-the-counter hearing aids are available without a prescription for adults with perceived mild to moderate hearing loss.

Physical activity

Physical activity is one of the best-supported habits for brain health. It improves blood flow, helps control blood pressure, blood sugar and weight, improves sleep and mood, and is linked to better thinking as people age. US guidelines recommend that adults get at least 150 minutes a week of moderate-intensity activity, such as brisk walking, plus muscle-strengthening activity on at least 2 days a week. Older adults should also include balance activities, which reduce the risk of falls and head injuries. Any amount is better than none, and starting later in life still helps.

Sleep

Sleep is when the brain consolidates memories, and ongoing short sleep is linked to poorer attention, memory and mood. Adults need 7 or more hours a night. A fixed wake time, daylight soon after waking, a cool and dark bedroom, and limiting caffeine later in the day all help. Loud snoring, gasping during sleep and daytime sleepiness can point to sleep apnea, a common and treatable condition that often shows up as trouble concentrating. Tell your doctor about these symptoms rather than accepting tiredness as normal, and avoid relying on alcohol or sleep aids to fall asleep.

Food and supplements

The evidence supports overall eating patterns rather than single foods or supplements. Mediterranean-style patterns, rich in vegetables, fruit, whole grains, beans, nuts, olive oil and fish, with limited red meat and processed food, are the best studied and are linked to better brain health. Vitamin B12 deficiency is a reversible cause of memory and thinking problems. Adults need 2.4 mcg a day, and people over 50, vegans and those taking metformin or acid-reducing medicines long term are more likely to run low. Supplements marketed for memory have no reliable evidence of benefit in people who are not deficient, and some interact with medicines.

Connection, learning, mood, smoking and alcohol

Social isolation is linked to higher dementia risk in its own right, and staying socially engaged and learning genuinely new and challenging skills are linked to better cognitive health. Brain-training games mainly improve performance at the game itself. Depression affects memory and concentration and is treatable, so do not dismiss it. Smoking damages blood vessels in the brain, and quitting helps at any age. Heavy drinking directly harms the brain; if you drink, keep to no more than 2 drinks a day for men or 1 for women, and less is better.

Stroke: recognizing it and acting fast

A stroke happens when blood supply to part of the brain is cut off, either by a clot blocking an artery, which is the most common type, or by a blood vessel bursting and bleeding into the brain. Brain cells in the affected area begin to die within minutes. Treatments that dissolve or remove clots can greatly reduce disability, but they only work within a window of hours, and the sooner they start the better. Every minute counts.

F.A.S.T. is the simplest way to remember the warning signs. Face drooping: one side of the face droops or feels numb, and the smile is uneven. Arm weakness: one arm is weak or numb and drifts down when both are raised. Speech difficulty: speech is slurred, strange or hard to understand. Time to call 911: call immediately, even if the symptoms go away, and note the time they started. Other sudden signs include numbness on one side of the body, confusion, trouble seeing in one or both eyes, loss of balance or coordination, and a sudden severe headache with no known cause.

Call 911 rather than driving the person to the hospital yourself. Emergency crews can begin assessment on the way and alert the hospital, which speeds up treatment. A transient ischemic attack, or TIA, sometimes called a mini-stroke, causes the same symptoms but they go away. It is still an emergency, because the risk of a full stroke is high in the days that follow. The main risk factors you can work on are high blood pressure, the biggest single one, atrial fibrillation, smoking, diabetes, high cholesterol and physical inactivity.

After a stroke

Recovery often continues for months, and rehabilitation with physical, occupational and speech therapists helps the brain rewire and relearn skills. Depression is common after a stroke and treatable. Preventing a second stroke means taking medicines as prescribed, which may include blood thinners, blood pressure and cholesterol medicines, along with not smoking and staying active. If you have palpitations or have been told you have an irregular heartbeat, make sure your doctor knows, because atrial fibrillation greatly raises stroke risk and treatment lowers it.

Headaches and migraine

Most headaches are not dangerous. Tension-type headaches cause a pressing or tight band of pain on both sides of the head and usually respond to rest and simple pain relievers. Migraine is a neurological condition, not just a bad headache: attacks typically cause throbbing pain, often on one side, with nausea and sensitivity to light and sound, and can last hours to days. Some people have an aura beforehand, usually visual changes such as zigzag lines or blind spots, though aura can also affect sensation or speech.

Migraine is disabling, underdiagnosed and undertreated. Acute treatment works best taken at the very start of an attack, so waiting to see whether a headache develops often means the medicine works less well. Using pain relievers on many days each month can lead to medication overuse headache, in which the treatment itself keeps headaches going; if you are taking pain relievers often, talk to your doctor. People with frequent attacks can be offered preventive treatment, and several newer options designed specifically for migraine are available.

Keeping a headache diary helps you and your doctor spot triggers and patterns, and count the days you take medicine. Common triggers include irregular sleep, skipped meals, dehydration, stress and its release, hormonal changes around menstruation, alcohol and some foods. People who have migraine with aura are generally advised not to use birth control containing estrogen, because it can raise stroke risk; talk to your doctor about alternatives.

Headaches that need urgent care

Call 911 for a sudden, severe headache that reaches its peak within seconds to minutes, often described as the worst headache of your life, and for headache with fever and a stiff neck or a rash, or with weakness, numbness, confusion, trouble speaking or loss of vision. See your doctor promptly for a new kind of headache after age 50, a headache that is worse lying down or when coughing or straining, headache during pregnancy or after giving birth, headache after a head injury, or any clear change in your usual pattern.

Head injuries and concussion

A concussion is a mild traumatic brain injury caused by a bump, blow or jolt to the head, or a hit to the body that makes the head move rapidly back and forth. You do not need to be knocked out to have a concussion. Symptoms can appear right away or over the following hours or days, and include headache, feeling foggy or slowed down, trouble concentrating or remembering, dizziness, nausea, sensitivity to light or noise, sleep changes and irritability. Most people recover within days to weeks, but some take longer.

Anyone with a suspected concussion during sport or play should be removed from activity right away and should not return the same day. A health care provider should check them, and the return to school, work and sport should be gradual, step by step, with symptoms guiding the pace. Rest for the first day or two is sensible, but long periods of complete rest in a dark room can slow recovery, so light activity is gradually reintroduced. Avoid alcohol while recovering, and do not return to contact sport until a provider has cleared you, because a second injury before the brain has healed can be serious. Call 911 or go to the emergency room after any head injury with the danger signs listed below.

Prevention is simple and effective: wear a seat belt, use the right helmet for biking, skating, skiing and contact sports, and make homes safer for children and older adults. Falls are a leading cause of head injury in older adults, so strength and balance exercise, a medicine review, eyesight checks, good lighting and removing trip hazards all protect the brain as well as the bones.

• Loss of consciousness, even briefly
• A headache that gets worse and does not go away
• Repeated vomiting, or a seizure
• Weakness, numbness, or decreased coordination
• Slurred speech, or increasing confusion, restlessness or agitation
• Unusual drowsiness or being unable to wake up
• One pupil larger than the other
• Any head injury in someone taking blood thinners, however well they seem

Seizures and epilepsy

A seizure is a burst of abnormal electrical activity in the brain. It can cause jerking movements and loss of consciousness, but many seizures are subtler: staring spells, brief confusion, unusual sensations or repetitive movements such as lip smacking. A single seizure can be triggered by a fever in a young child, low blood sugar, alcohol withdrawal or a head injury. Epilepsy is diagnosed when someone has a tendency to have recurrent seizures, and it is based on the person's history and an eyewitness account, supported by an EEG, which records the brain's electrical activity, and brain imaging.

Many people with epilepsy become seizure-free with medicine. The practical risks are where harm usually happens: missed doses, lack of sleep, alcohol, driving, swimming or bathing alone, and heights. Take medicine at the same times every day and never stop or change it without talking to your neurologist. Driving rules depend on your state and usually require a seizure-free period. Some seizure medicines, valproate in particular, carry serious risks in pregnancy, so anyone who could become pregnant should discuss birth control and pregnancy plans with their neurologist early.

Knowing basic seizure first aid can prevent injury. Stay with the person and time the seizure. Move hard or sharp objects away and cushion their head. Once the jerking stops, or if they are not fully awake, turn them gently onto their side to help keep the airway clear. Loosen anything tight around the neck. Stay with them until they are fully alert, and speak calmly as they come round.

• Do not hold the person down or try to stop their movements
• Do not put anything in their mouth; they cannot swallow their tongue
• Do not give food, drink or pills until they are fully awake
• Call 911 if a seizure lasts more than 5 minutes, another follows without recovery in between, it is a first-ever seizure, it happens in water, the person is injured, pregnant or has diabetes, or they have trouble breathing or do not wake up afterward

Brain health at different stages of life

Brain development begins before birth. During pregnancy, there is no known safe amount of alcohol, and a daily folic acid supplement, recommended for anyone who could become pregnant, helps prevent serious birth defects of the brain and spine. Get prompt care for a severe headache, vision changes or sudden swelling during pregnancy or in the weeks after birth, as these can be signs of high blood pressure conditions that affect the brain. People with epilepsy should plan pregnancy with their neurologist.

Children and teens need more sleep than adults, roughly 9 to 12 hours for school-age children and 8 to 10 for teens, and short sleep shows up as poor attention, mood and learning. Daily physical activity, protection from head injuries in sport, and reading and talking with young children all support development. Talk to your child's doctor about any concerns with speech, learning, behavior or development; early support makes a difference.

For older adults, the priorities are controlling blood pressure, correcting hearing and vision, staying active and connected, preventing falls, and reviewing medicines regularly. Some common medicines, including certain sleep aids, allergy medicines and bladder medicines, can affect memory and raise the risk of confusion and falls in older people, so ask your doctor or pharmacist to review everything you take at least once a year. People with diabetes, heart disease or atrial fibrillation have higher risks of stroke and cognitive decline, which makes managing those conditions part of protecting the brain.

Checkups, costs and talking to your doctor

Brain health is part of routine care, not something to raise only when there is a crisis. A yearly checkup is a chance to check blood pressure, blood sugar and cholesterol, review medicines, ask about hearing, sleep and mood, and mention any changes in memory. If you have Medicare, the yearly Annual Wellness Visit includes a check for cognitive impairment and a personalized prevention plan at no cost to you when your provider accepts assignment. Medicare also covers a separate visit for a detailed cognitive assessment and care planning if memory problems are suspected.

When you raise a concern, be specific. Describe what has changed, when you first noticed it, whether it is getting worse, and how it affects daily life, such as missing bills or getting lost while driving. Bring a family member or friend. Ask what could be causing the problem, which tests are needed, whether any of your medicines could contribute, and what to watch for next. If you are diagnosed with a condition, ask for written information and what support is available locally.

Mental health is brain health

Depression, anxiety and other mental health conditions affect concentration, memory, sleep and motivation, and they are common and treatable. If low mood, hopelessness or loss of interest has lasted more than a couple of weeks, talk to your doctor. If you are thinking about suicide or are worried about someone else, call or text 988 to reach the 988 Suicide & Crisis Lifeline, available 24 hours a day. If someone is in immediate danger, call 911.

Myths and what the guidance actually says

Brain health is heavily marketed, and fear of dementia makes people vulnerable to promises. At the same time, fatalism stops people from doing the things that are genuinely linked to better outcomes. The list below sets common beliefs against what US guidance and research support. The pattern is consistent: the evidence favors broad, ordinary habits over products, and early checkups over waiting.

• Myth: dementia is a normal part of aging. Guidance: some slowing is normal, but memory loss that disrupts daily life is not and should be checked.
• Myth: nothing can be done to lower dementia risk. Guidance: blood pressure, hearing, activity, smoking and other factors are linked to risk and can be changed.
• Myth: memory supplements protect the brain. Guidance: there is no reliable evidence of benefit in people who are not deficient.
• Myth: brain-training apps keep your mind sharp. Guidance: they mainly improve performance at the game itself; learning new skills and staying social are better supported.
• Myth: if stroke symptoms go away, there is no need to call 911. Guidance: a TIA is an emergency, because the risk of a full stroke is high in the following days.
• Myth: you need to be knocked out to have a concussion. Guidance: most concussions happen without loss of consciousness.
• Myth: you should put something in a person's mouth during a seizure. Guidance: never do this; turn them on their side and protect their head.

A practical four-week plan

Brain health is built from many small habits rather than one big change. This plan takes one area a week, starting with the steps most clearly linked to stroke and dementia risk. Over the longer term, have your blood pressure checked at least yearly, review your medicines with your doctor or pharmacist each year, get your hearing tested if you notice changes, and keep learning, moving and seeing people.

• Week 1, know your numbers: get your blood pressure checked and ask when your blood sugar and cholesterol were last tested. Learn F.A.S.T. and make sure everyone in your household knows to call 911 for stroke symptoms.
• Week 2, sleep: set a fixed wake time, get daylight soon after waking, and aim for 7 or more hours in bed asleep. If you snore loudly and wake unrefreshed, book a visit about sleep apnea.
• Week 3, move and connect: build toward 150 minutes of moderate activity a week, add two strength sessions, and plan at least one social activity or new learning challenge each week.
• Week 4, check and protect: book a hearing test if you have any doubts, ask for a medicine review, check that helmets fit, and if you or someone close to you has noticed memory changes, make an appointment to talk them through.

Every guide in this topic

• Dementia Risk Reduction: What Published Guidance Supports
• The Evidence on Memory Problems, Without the Hype
• Stroke: What Published Guidance Supports
• Migraine: What the Evidence Actually Says
• Concussion: What Published Guidance Supports
• What the Guidance Really Says About Sleep and the Brain
• Cognitive Activity: What the Evidence Actually Says
• Epilepsy: Sorting the Evidence From the Noise
• Hearing and the Brain: Sorting the Evidence From the Noise
• The Evidence on Brain and Diet, Without the Hype

Frequently asked questions

Is forgetting things a sign of dementia?

Not usually. Occasionally forgetting names or misplacing things is common at every age. What matters is whether memory or thinking problems are interfering with daily life, such as repeating questions, getting lost on familiar routes or losing track of bills. If that is happening, see your doctor. Many causes, including depression, thyroid problems, B12 deficiency and medicines, are treatable.

What should I do if I think someone is having a stroke?

Call 911 immediately. Use F.A.S.T.: face drooping, arm weakness, speech difficulty, time to call 911. Note the time symptoms started, because treatment decisions depend on it. Do not drive the person to the hospital yourself, and do not wait to see whether symptoms go away. Even symptoms that disappear can signal a TIA, which needs emergency assessment.

Can I lower my risk of dementia?

No one can guarantee it, but research links a meaningful share of risk to factors you can change. Control your blood pressure, get hearing loss treated, stay physically active, do not smoke, limit alcohol, manage diabetes, sleep well and stay socially and mentally engaged. These habits also lower stroke and heart disease risk, so they are worthwhile whatever your family history.

Do memory supplements or brain games work?

Supplements marketed for memory have no reliable evidence of benefit in people who are not deficient, and some interact with medicines. Brain-training games mainly make you better at the game itself. Better-supported options are learning genuinely new skills, staying socially active, exercising regularly and having your doctor check for deficiencies such as low vitamin B12.

When is a headache an emergency?

Call 911 for a sudden, severe headache that peaks within seconds to minutes, or a headache with fever and a stiff neck, a rash, weakness, numbness, confusion, trouble speaking or vision loss. See your doctor promptly for a new kind of headache after 50, headache that is worse lying down or when coughing, or headache during or soon after pregnancy.

How long should I rest after a concussion?

Rest for the first day or two, then gradually return to light activity as symptoms allow. Long periods of complete rest in a dark room can slow recovery. Return to school, work and sport step by step with a health care provider's guidance, and never return to sport the same day as the injury. Get emergency care for worsening symptoms.

What should I do if someone has a seizure?

Stay with them, time the seizure, move sharp objects away and cushion their head. Do not hold them down or put anything in their mouth. Turn them onto their side once the jerking stops. Call 911 if it lasts more than 5 minutes, it is a first seizure, another follows, it happens in water, or they are injured or do not wake up.

Does hearing loss really affect the brain?

Untreated hearing loss is linked to a higher risk of dementia, as well as social isolation and low mood. Treating it is one of the changeable factors recommended for brain health. Get a hearing test if you or others notice you are missing things, and wear hearing aids consistently. Over-the-counter hearing aids are available for adults with perceived mild to moderate hearing loss.

Are the new Alzheimer's drugs right for everyone?

No. Lecanemab (Leqembi) and donanemab (Kisunla) are approved only for people with mild cognitive impairment or mild dementia due to Alzheimer's disease with confirmed amyloid in the brain. They modestly slow decline, require regular infusions or injections and MRI monitoring, and carry a risk of brain swelling or bleeding. A specialist can help you weigh the benefits and risks.

Does Medicare cover memory checks?

Yes. The Medicare Annual Wellness Visit includes a check for cognitive impairment, and Medicare also covers a separate, more detailed cognitive assessment and care planning visit if memory problems are suspected. Diagnostic tests your doctor orders are generally covered under Part B, with the usual cost-sharing. Ask your provider what you may need to pay before tests are done.

When to speak to a doctor

See your doctor for memory or thinking problems that affect daily life, getting lost in familiar places, personality change, a new kind of headache after age 50, frequent headaches or frequent pain reliever use, loud snoring with daytime sleepiness, or any suspected concussion. Get same-day care for sudden confusion, especially in an older adult, and for sudden hearing loss. Call 911 for face drooping, arm or leg weakness, slurred or confused speech, sudden vision loss or loss of balance, even if the symptoms go away; a sudden severe headache; a seizure lasting more than 5 minutes or a first seizure; or a head injury with loss of consciousness, repeated vomiting, worsening headache or increasing drowsiness. If you are having thoughts of suicide, call or text 988. For a suspected overdose or poisoning, call Poison Control at 1-800-222-1222, or 911 if the person is unresponsive or having trouble breathing.

Where this comes from

• National Institute on Aging — Cognitive Health and Older Adults
• National Institute on Aging — Memory Problems, Forgetfulness, and Aging
• American Stroke Association — Stroke Warning Signs and Symptoms
• American Heart Association — Understanding Blood Pressure Readings
• National Institute of Neurological Disorders and Stroke — Migraine
• CDC — Signs and Symptoms of Concussion
• CDC — Seizure First Aid
• CDC — About Sleep
• NIH Office of Dietary Supplements — Vitamin B12 Fact Sheet for Consumers
• Office of Disease Prevention and Health Promotion — Physical Activity Guidelines for Americans, 2nd edition

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.