Substance Use: The Complete Guide

A practical guide to alcohol, cannabis, nicotine, opioids, stimulants and other drugs: how substance use problems develop, how to lower the risks, how to respond to an overdose, and how to find treatment that works. It is for anyone worried about their own use or someone else's, and for parents, partners and friends who want to help.

Key numbers at a glance

How substance use affects the brain and body

Alcohol, nicotine, cannabis, opioids and stimulants are very different substances, but they share one feature: they act on the brain's reward system, the circuits that make eating, connection and other necessities feel good. Drugs can trigger that system more strongly and more quickly than everyday rewards. With repeated use, the brain adapts. It may become less responsive, so a person needs more of the substance to feel the same effect (tolerance), and feels unwell without it (withdrawal). Areas of the brain involved in judgment, planning and self-control can also be affected.

These changes help explain why addiction is not simply a matter of willpower. A substance use disorder is a medical condition in which a person keeps using alcohol or drugs despite harm to their health, work, relationships or safety, and finds it hard to cut down even when they want to. Like other chronic conditions such as diabetes or high blood pressure, it is shaped by genes, environment and behavior, it can be treated, and setbacks are common but do not mean treatment has failed.

Substance use also exists on a range. Not everyone who drinks or uses a drug has a disorder, and not every risky situation involves addiction. One night of binge drinking can lead to a crash, a fall or alcohol poisoning. One counterfeit pill can contain a lethal amount of fentanyl. Understanding both the long-term risk of addiction and the immediate risks of a single episode is the foundation for staying safer.

Who is at higher risk

Anyone can develop a substance use problem, but some factors raise the odds. A family history of addiction increases risk, partly through genes. Starting young is one of the strongest risk factors: the brain keeps developing until about age 25, and people who begin using alcohol, nicotine or cannabis in their early teens are more likely to develop problems later. Mental health conditions such as depression, anxiety, ADHD and post-traumatic stress disorder often occur alongside substance use, and each can make the other worse.

Life circumstances matter too. Trauma, chronic stress, isolation, chronic pain and easy access to substances all play a part. Some people first take opioids as prescribed after surgery or an injury, and find it hard to stop. Others start using stimulants to keep up with work or school. None of these routes reflects a weakness of character, and knowing your own risk factors can help you make choices with your eyes open.

The way a substance is used also changes the danger. Using alone, mixing substances, using after a period of not using (when tolerance has dropped), and buying pills or powders from unregulated sources all raise the risk of overdose. Mixing opioids with alcohol, benzodiazepines or sleep medicines is especially dangerous because each slows breathing. Combining stimulants with alcohol or opioids adds strain on the heart and can hide how intoxicated a person really is, which makes it harder to judge when to stop.

• Family history of substance use disorder
• Starting to use alcohol, nicotine, cannabis or other drugs before age 18
• Depression, anxiety, ADHD, trauma or other mental health conditions
• Chronic pain or long-term use of prescription opioids
• Using alone, mixing substances, or using after a break

Alcohol: drinking levels and alcohol use disorder

Alcohol is the most widely used substance in the US, and the risks are easy to underestimate. Start with what counts as a drink. A US standard drink contains 14 grams of pure alcohol, which is about 12 fl oz of regular beer, 5 fl oz of wine or 1.5 fl oz of distilled spirits. Many restaurant pours, craft beers and mixed drinks contain more than one standard drink, so counting glasses can undercount what you actually had.

The Dietary Guidelines for Americans advise that adults of legal drinking age who choose to drink should limit intake to 2 drinks or fewer in a day for men and 1 drink or fewer in a day for women, and that drinking less is better for health than drinking more. Some people should not drink at all, including anyone who is pregnant or might be, people under 21, people taking medicines that interact with alcohol, people with certain medical conditions, and people recovering from alcohol use disorder.

The National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines heavy drinking as 5 or more drinks on any day or 15 or more a week for men, and 4 or more on any day or 8 or more a week for women. Binge drinking, which typically means about 5 drinks for men or 4 for women in around 2 hours, raises the risk of injuries, violence and alcohol poisoning. Over time, heavy drinking is linked to liver disease, high blood pressure, heart problems, several cancers, and depression and anxiety.

Signs of alcohol use disorder

Alcohol use disorder is diagnosed by a health professional, but certain patterns are worth noticing. Do you often drink more or for longer than you meant to? Have you tried to cut down and could not? Do you spend a lot of time drinking or recovering? Has drinking caused problems at home, at work or with your health, yet you keep going? Do you need more to feel the effect, or feel shaky, sweaty, anxious or unable to sleep when it wears off? The more of these apply, the more likely a problem is, and the more useful a conversation with your doctor will be.

Why stopping suddenly can be dangerous

If you have been drinking heavily every day, stopping abruptly can trigger alcohol withdrawal, which in severe cases causes seizures, hallucinations and a life-threatening condition called delirium tremens. This is not a reason to keep drinking; it is a reason to stop with medical help. Your doctor can assess your risk and arrange safe, supervised withdrawal, sometimes at home with medicines and close follow-up, and sometimes in a hospital or treatment program.

Cannabis, nicotine and vaping

Cannabis is legal for adults in many states, but legal does not mean risk-free. About 3 in 10 people who use marijuana have cannabis use disorder, and the risk is higher for people who start before age 18 or use it daily. Today's products are often much more potent than in the past. Cannabis slows reaction time and impairs coordination, so driving after using it is dangerous. No amount is known to be safe during pregnancy or breastfeeding. Some people who use cannabis heavily and regularly develop repeated bouts of severe vomiting, which should be checked by a doctor.

Edibles deserve special care. They can take 30 minutes to 2 hours to take effect, so people sometimes take more before the first dose kicks in and end up with severe anxiety, confusion, vomiting or a racing heart. Many edibles look like ordinary candy, cookies or gummies, and children who eat them can become very sleepy or have trouble breathing. Store all cannabis products locked up and out of reach, and call Poison Control at 1-800-222-1222 if a child or pet eats one.

Nicotine is highly addictive in any form. E-cigarettes are the most commonly used tobacco product among US middle and high school students, and nicotine can harm the developing brain, which continues to mature until about age 25. The aerosol from vapes can contain harmful substances, including heavy metals and cancer-causing chemicals. The federal minimum age to buy any tobacco product, including e-cigarettes, is 21. E-liquids are poisonous if swallowed, so keep them locked away from children.

Quitting nicotine

Most people who smoke or vape want to quit, and many need several attempts before it sticks. Your chances improve when you combine counseling with medicine. For adults, FDA-approved quit-smoking medicines include nicotine replacement therapy (patches, gum and lozenges, some available without a prescription) and prescription medicines such as varenicline and bupropion. Free coaching is available by calling 1-800-QUIT-NOW (1-800-784-8669) or through smokefree.gov. Teens should talk to their doctor about the right approach for them. Switching from cigarettes to e-cigarettes is not the same as quitting, and using both keeps you exposed to the harms of smoking.

Opioids, fentanyl and stimulants

Opioids include prescription pain medicines such as oxycodone, hydrocodone and morphine, as well as heroin and fentanyl. They relieve pain and can cause a sense of calm or euphoria, but in higher doses they slow and then stop breathing. That is how an opioid overdose kills. Taking opioids as prescribed for a short time after surgery or injury is generally safe for most people, but long-term use raises the risk of dependence and opioid use disorder. Never take more than prescribed, never mix opioids with alcohol or sedatives, and never share them.

Illegally made fentanyl is now the main driver of overdose deaths in the US. It is about 50 times stronger than heroin and 100 times stronger than morphine, so a very small amount can be fatal. It is mixed into heroin, cocaine and methamphetamine, and pressed into counterfeit pills made to look exactly like real prescription medicines such as pain relievers, anxiety medicines and ADHD stimulants. You cannot see, smell or taste fentanyl. Fentanyl test strips can detect it in drugs. The safest rule is simple: only take pills prescribed for you and dispensed by a licensed pharmacy.

Stimulants include cocaine, methamphetamine and prescription stimulants used without a prescription. They raise heart rate, blood pressure and body temperature, and can cause heart attacks, strokes, seizures, paranoia and psychosis. Because stimulants are now often contaminated with fentanyl, people who use them can overdose on opioids without knowing it, so naloxone can still be needed. Contingency management, a behavioral therapy that gives tangible rewards for drug-free tests, and other counseling approaches are the main treatments; there are currently no FDA-approved medicines for stimulant use disorder.

• Only take medicines prescribed for you, from a licensed pharmacy
• Never take pills bought from friends, online sellers or social media, even if they look real
• Do not use drugs alone, and do not mix them with each other or with alcohol
• Carry naloxone and make sure people around you know where it is
• Keep prescription opioids and stimulants locked up, and dispose of leftovers safely

Safe storage of medicines

Leftover prescription opioids in home medicine cabinets are a common source of misuse and accidental poisoning. Teens and visitors may take them, and young children can be seriously harmed by swallowing even one pill, including medicines used to treat opioid use disorder. Store opioids, stimulants, sedatives and cannabis products locked up and out of sight and keep track of how many pills are left in each bottle so you notice if any go missing.

Safe disposal of leftover medicines

When you no longer need a medicine, get rid of it promptly. The best option is a drug take-back site, kiosk or event; many pharmacies and police stations have year-round kiosks, and some pharmacies offer mail-back envelopes. If take-back is not available, most medicines can go in household trash: mix them with something unappealing such as used coffee grounds or cat litter, seal them in a bag and throw it away. FDA lists certain medicines, such as some opioids, that should be flushed if take-back is not available. Fentanyl patches should be folded with the sticky sides together before flushing. Do not flush medicines that are not on the FDA flush list. Clean out your medicine cabinet at least once a year, scratch out personal information on labels before throwing bottles away, and never give leftover medicines to friends or family. If someone swallows a medicine by mistake, call Poison Control at 1-800-222-1222, even if they seem fine.

Recognizing and responding to an overdose

An overdose is a medical emergency, and what bystanders do in the first few minutes can decide whether someone lives. With opioids, the danger is slowed or stopped breathing. Signs include pinpoint pupils, being unresponsive or unable to wake, slow or stopped breathing, choking or gurgling sounds, and blue or gray lips and fingertips. Do not assume the person is just sleeping it off.

Naloxone is a medicine that can quickly reverse an opioid overdose by knocking opioids off the receptors in the brain. It comes as a nasal spray or an injection, and FDA approved naloxone nasal spray for sale without a prescription in 2023, so you can buy it at most pharmacies. It is safe to give even if you are not sure the person took opioids. If there is no response after 2 to 3 minutes, a second dose may be needed, and with fentanyl more than one dose is sometimes required.

Naloxone can wear off before the opioid does, so the overdose can return even after the person wakes up. That is why calling 911 matters even when naloxone works. Stimulant overdoses look different: chest pain, very high body temperature, severe agitation, confusion, seizures or signs of stroke. Alcohol poisoning can cause confusion, vomiting, seizures, slow or irregular breathing, cold or bluish skin and being impossible to wake. In every case, call 911.

• Call 911 first, then give naloxone if opioids might be involved
• Try to keep the person breathing; if trained, give rescue breaths or CPR
• Lay the person on their side to prevent choking if they are breathing
• Give a second dose of naloxone after 2 to 3 minutes if there is no response
• Stay with the person until emergency help arrives, and tell responders what was taken
• Do not put the person in a cold bath, try to make them vomit or leave them alone

Good Samaritan laws

Fear of the police stops some people from calling for help. Many states have Good Samaritan laws that offer some legal protection to people who call 911 for an overdose and to the person who overdosed. The details vary from state to state, so it is worth learning your state's rules. Whatever the law where you live, a call for help is what gives the person the best chance of surviving.

Screening and how to talk to your doctor

The US Preventive Services Task Force recommends that primary care providers screen adults 18 and older for unhealthy alcohol use, and offer brief counseling to people who drink at risky levels. It also recommends screening adults for unhealthy drug use when services for accurate diagnosis and care can be offered. In practice, your doctor may ask a short set of questions at a checkup, such as how often you drink and how many drinks you have on a typical day, or how many times in the past year you had several drinks in a single day.

Answering honestly helps your doctor give you safer care. Alcohol and drugs interact with many medicines, affect blood pressure, sleep, mood and blood sugar, and change how anesthesia works. Your health information is private, and federal law gives substance use treatment records extra confidentiality protections. A good clinician will not judge you; they want to know so they can help.

If you are worried about your own use, you can bring it up directly. Saying "I think I am drinking too much and I want help cutting down" or "I have been taking more of my pain medicine than prescribed" is enough to start the conversation. Your doctor can check for health effects, discuss medicines that reduce cravings, help you withdraw safely, and refer you to counseling or specialty treatment if needed.

• How much and how often you drink or use, including cannabis and nicotine
• Any prescription medicines you take more of, or differently, than prescribed
• Withdrawal symptoms such as shakiness, sweating, anxiety or poor sleep when you stop
• Mood, sleep and any thoughts of self-harm
• What you want: to cut down, to stop, or to understand your options

Treatment that works

Substance use disorders are treatable, and there is no single right path. Treatment is matched to the person and the substance, and may include medicines, behavioral therapies, mutual-support groups and help with housing, work or mental health. Levels of care range from regular visits with a primary care provider, through outpatient and intensive outpatient programs, to residential treatment. Most people do not need to start with the most intensive option.

For opioid use disorder, medicines are the most effective treatment. Methadone is given through certified opioid treatment programs. Buprenorphine can be prescribed by any clinician with the right DEA registration, including many primary care providers. Extended-release naltrexone is a monthly injection; you must be opioid-free for a period before starting it. These medicines lower the risk of overdose death and help people stay in recovery, and the length of treatment is decided with your care team; there is no set time limit. Counseling is recommended alongside medicine. Using medicine to treat opioid use disorder is recovery, not a substitute addiction.

For alcohol use disorder, FDA-approved medicines include naltrexone, acamprosate and disulfiram. They can reduce cravings, help prevent relapse or discourage drinking, and they can be prescribed by a primary care provider. Behavioral therapies such as cognitive behavioral therapy, motivational interviewing and contingency management help people build skills, change patterns and strengthen motivation. Mutual-support groups offer ongoing connection, and many people find them valuable alongside professional care.

Treating mental health at the same time

Many people with a substance use disorder also live with depression, anxiety, PTSD, bipolar disorder or another mental health condition. Treating both together tends to work better than treating one and hoping the other improves. When you look for a program, ask whether it offers care for co-occurring mental health conditions, and tell your clinicians about any mental health diagnosis or symptoms you have.

Recovery and setbacks

Recovery is usually a process rather than a single event. Returning to use after a period of not using is common, and it is a signal to adjust treatment rather than a sign of failure. It is also a time of high overdose risk, because tolerance drops during periods without opioids, and an amount a person once used can now be fatal. If you or someone you love is in recovery from opioid use, keep naloxone on hand and avoid using alone.

Finding help and paying for treatment

Knowing where to start is one of the biggest barriers to getting help. Your primary care provider is a good first step: they can assess you, start some medicines, and refer you. The SAMHSA National Helpline, 1-800-662-HELP (1-800-662-4357), is free, confidential and open 24 hours a day, every day, in English and Spanish, and can point you to local services. FindTreatment.gov lets you search for licensed treatment facilities by location, type of care, payment options and whether they offer medicines.

Most health plans, including Medicaid, Medicare and Marketplace plans, cover substance use treatment, though the details vary. Before choosing a program, call your insurer or Medicaid plan to ask what is covered, whether you need prior approval, and which programs are in network. If you have no insurance, ask programs about sliding-scale fees, and check whether you might qualify for Medicaid. Many people do not realize they are eligible.

Be cautious with programs that promise a quick cure, guaranteed results or a fixed number of days that will "fix" addiction, and with programs that discourage proven medicines. A quality program should assess you individually, offer or connect you with medicines when appropriate, treat co-occurring mental health conditions, and plan for ongoing support after any intensive phase ends. The NIAAA Alcohol Treatment Navigator can help you evaluate options for alcohol problems.

• Does the program offer medicines for opioid or alcohol use disorder, or work with prescribers who do?
• Is it licensed or accredited, and are staff trained in substance use care?
• Does it treat co-occurring mental health conditions?
• What does it cost, and what will your insurance or Medicaid pay?
• What support does it offer after the program ends?

Specific groups: teens, pregnancy and older adults

Teens are especially vulnerable because their brains are still developing and because counterfeit pills are sold through social media and messaging apps. Talk with young people early and often, and listen to their reasons for using, whether stress, curiosity or fitting in. Explain clearly that any pill not from a pharmacy could contain fentanyl. Keep alcohol, cannabis and prescription medicines locked up at home, and ask your child's doctor about screening and support. Pediatricians can help with vaping, alcohol and other drug concerns.

During pregnancy, no amount of alcohol is known to be safe, and no amount of cannabis is known to be safe during pregnancy or breastfeeding. Smoking and vaping nicotine are also harmful. If you are pregnant and using opioids, do not stop suddenly on your own; tell your obstetric care provider. Treatment with methadone or buprenorphine is recommended for opioid use disorder during pregnancy, and it is safer for both you and the baby than continued use or unsupervised withdrawal.

Older adults are more sensitive to alcohol because the body processes it more slowly with age, and alcohol interacts with many medicines commonly taken later in life, including sleep aids, pain relievers, anxiety medicines and blood thinners. It also raises the risk of falls. Older adults may benefit from drinking less than the general limits, or not at all; ask your doctor what is safe for you. Misuse of prescription opioids and sedatives can also go unnoticed in this group, so medicine reviews at checkups are worth doing.

Supporting someone you care about

Watching someone you love struggle with alcohol or drugs is painful, and it is natural to feel angry, frightened or helpless. Remember that addiction is a treatable medical condition, not a moral failing. Shaming, threatening or lecturing rarely works and can push people away. Choose a time when they are sober, talk calmly, use "I" statements that describe what you have seen and how you feel, and make it clear that you care and that help is available.

Some approaches are designed specifically for families. Community Reinforcement and Family Training (CRAFT), for example, teaches family members ways to encourage a loved one to enter treatment while improving their own wellbeing. Learn about treatment options ahead of time so you are ready when your loved one says yes. Avoid covering up or paying for the consequences of drug use, which can make it easier for the problem to continue.

Practical safety steps matter too. Keep naloxone at home and learn how to use it. Store medicines, including your own, securely, and dispose of leftovers. Look after your own health by getting counseling or joining a family support group; the SAMHSA National Helpline also helps family members. If your loved one talks about suicide, call or text 988. If there is violence at home, get to safety and call 911.

A 4-week plan to cut down or get help

If you want to change your drinking or drug use, a short, concrete plan can help you move from worry to action. This plan is a starting point, not a substitute for medical care. If you drink heavily every day, or use opioids, benzodiazepines or other sedatives regularly, talk to your doctor before cutting back, because stopping suddenly can be dangerous.

• Week 1: keep an honest daily record of what you drink or use, when and why; learn what a standard drink is; get naloxone if opioids are involved in any way
• Week 2: book an appointment with your doctor or call the SAMHSA National Helpline at 1-800-662-4357; set a specific goal, such as alcohol-free days or a daily limit
• Week 3: remove alcohol or drugs from your home, plan for high-risk situations, and tell one trusted person about your goal; ask your doctor about medicines that reduce cravings
• Week 4: review your record and progress; if cutting down has been hard, consider counseling, a support group or a treatment program found through FindTreatment.gov
• Ongoing: keep follow-up appointments, look after sleep and mental health, and treat setbacks as information rather than failure

Every guide in this topic

• What the Guidance Really Says About Opioid Overdose and Naloxone
• Fentanyl Risks: What the Evidence Actually Says
• The Evidence on Alcohol Use Disorder, Without the Hype
• The Evidence on Cannabis Use, Without the Hype
• What the Guidance Really Says About Vaping and E-Cigarettes
• What the Guidance Really Says About Stimulant Use
• Medications for Opioid Use Disorder: What Published Guidance Supports
• Finding Substance Use Treatment: What Published Guidance Supports
• Supporting a Family Member With Addiction: Sorting the Evidence From the Noise
• The Evidence on Safe Disposal of Medicines, Without the Hype

Frequently asked questions

How do I know if my drinking is a problem?

Warning signs include drinking more or longer than you meant to, failing to cut down, spending a lot of time drinking or recovering, and continuing despite problems with health, work or relationships. Heavy drinking means 5 or more drinks on any day or 15 a week for men, and 4 or more on any day or 8 a week for women. Your doctor can screen you and discuss options.

Is it safe to stop drinking on my own?

If you drink lightly or occasionally, cutting back is usually safe. If you have been drinking heavily every day, stopping suddenly can cause dangerous withdrawal, including seizures and hallucinations. Talk to your doctor first so they can assess your risk and arrange supervised withdrawal if needed. Call 911 for seizures, confusion or hallucinations.

Where can I get naloxone, and do I need a prescription?

Naloxone nasal spray has been approved by FDA for sale without a prescription since 2023, so you can buy it at most pharmacies. Some health departments and community programs give it out free. Keep it at home and carry it if you or someone you know uses opioids or any drug that could contain fentanyl, and make sure others know where it is.

What should I do if someone is overdosing?

Call 911, then give naloxone if opioids might be involved. Try to keep the person breathing, lay them on their side if they are breathing, and give a second dose after 2 to 3 minutes if there is no response. Stay with them until help arrives, because naloxone can wear off before the opioid does and the overdose can return.

Why are counterfeit pills so dangerous?

Counterfeit pills are made to look like real prescription medicines but often contain illegally made fentanyl, which is about 50 times stronger than heroin. You cannot see, smell or taste it, and one pill can be fatal. Only take pills prescribed for you and dispensed by a licensed pharmacy, and never take pills from friends, online sellers or social media.

Is medicine for opioid use disorder just replacing one drug with another?

No. Methadone, buprenorphine and naltrexone are FDA-approved treatments that lower the risk of overdose death and help people stay in recovery. Taken as prescribed, they stabilize brain chemistry rather than producing a high, so people can work, care for family and rebuild their lives. Using medicine to treat opioid use disorder is recovery, just as insulin is treatment for diabetes.

Is cannabis addictive?

It can be. About 3 in 10 people who use marijuana have cannabis use disorder, and the risk is higher for people who start before 18 or use it daily. Signs include using more than intended, failing to cut down and continuing despite problems. Cannabis also impairs driving, and no amount is known to be safe during pregnancy or breastfeeding.

How can I help my teen avoid vaping and drugs?

Talk early and often, ask open questions and listen to their reasons. Explain that nicotine harms the developing brain, that the legal age to buy vapes is 21, and that any pill not from a pharmacy could contain fentanyl. Keep alcohol, cannabis and medicines locked up, set clear expectations, and ask your child's doctor for support if you are worried.

Does insurance cover addiction treatment?

Most health plans, including Medicaid, Medicare and Marketplace plans, cover substance use treatment, though benefits and networks vary. Call your insurer or Medicaid plan to ask what is covered and whether prior approval is needed. If you are uninsured, ask programs about sliding-scale fees and check whether you qualify for Medicaid. The SAMHSA National Helpline can help you find options.

How do I help a family member who does not want help?

Stay connected, talk calmly when they are sober, and use "I" statements about what you have seen. Learn about treatment so you are ready when they are. Approaches such as CRAFT help families encourage treatment. Keep naloxone at home, avoid covering for consequences, and get support for yourself through counseling, family groups or the SAMHSA National Helpline.

When to speak to a doctor

See your doctor if you are worried about your drinking or drug use, find it hard to cut down, or want to stop after heavy daily use of alcohol, benzodiazepines or opioids, since withdrawal can be dangerous. Call 911 right away for an overdose or suspected overdose: someone who cannot be woken, has slow or stopped breathing, blue or gray lips, seizures, chest pain, very high body temperature, severe confusion or signs of stroke; give naloxone if opioids might be involved and stay with the person. Call Poison Control at 1-800-222-1222 if a child swallows a medicine, cannabis edible or e-liquid, even if they seem fine. If you or someone else is thinking about suicide or is in crisis, call or text 988 to reach the 988 Suicide & Crisis Lifeline. For free, confidential treatment referrals, call the SAMHSA National Helpline at 1-800-662-4357.

Where this comes from

• CDC — Preventing Opioid Overdose
• CDC — Fentanyl Facts
• FDA — Information about Naloxone and Nalmefene
• National Institute on Alcohol Abuse and Alcoholism — Understanding Alcohol Use Disorder
• National Institute on Alcohol Abuse and Alcoholism — What Is A Standard Drink?
• Dietary Guidelines for Americans — Dietary Guidelines for Americans, 2020-2025
• National Institute on Drug Abuse — Medications to Treat Opioid Use Disorder
• National Institute on Drug Abuse — Cannabis (Marijuana)
• US Preventive Services Task Force — Unhealthy Alcohol Use in Adolescents and Adults: Screening and Behavioral Counseling Interventions
• SAMHSA — National Helpline

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.