Thyroid and Hormones: The Complete Guide

How your thyroid and other hormone glands work, how to read thyroid tests, and what to know about underactive and overactive thyroid, thyroid lumps, iodine, adrenal conditions, PCOS, birth control and menopause. For anyone with symptoms they suspect are hormonal, a thyroid diagnosis, or questions about hormone treatment.

Key numbers at a glance

How your hormone system works

Hormones are chemical messengers. Glands release them into the blood, and they travel to distant organs to switch processes on or off. Your endocrine system includes the thyroid in the front of your neck, the adrenal glands on top of your kidneys, the pituitary gland at the base of your brain, the parathyroid glands behind the thyroid, the pancreas, and the ovaries or testes. Between them they control your energy use, growth, blood pressure, blood sugar, calcium balance, fertility and response to stress.

Most hormones are regulated by feedback loops, much like a thermostat. The thyroid is a good example. When thyroid hormone levels fall, the pituitary gland releases more thyroid-stimulating hormone (TSH) to push the thyroid to work harder. When levels rise, the pituitary eases off and TSH falls. This explains the single most confusing thing about thyroid tests: TSH moves in the opposite direction to the thyroid hormone it controls, so a high TSH usually means an underactive thyroid.

The thyroid itself is a butterfly-shaped gland that uses iodine from your diet to make two hormones, thyroxine (T4) and triiodothyronine (T3). T4 is the main product and is converted into the more active T3 in tissues around the body. Thyroid hormone sets the pace of metabolism in almost every cell, which is why too little or too much affects so many systems at once, from heart rate and body temperature to bowel habits, mood, skin and menstrual cycles.

Why hormone problems are easy to miss, and easy to over-blame

Hormone conditions often produce vague symptoms that develop slowly: tiredness, weight change, low mood, feeling cold or hot, poor sleep, changes in periods. These are also the symptoms of ordinary life, stress, aging, poor sleep and many other conditions, so thyroid disease in particular is frequently missed for months or years. A simple blood test can settle the question, which is why it is worth asking for one if your symptoms are persistent or unexplained.

The opposite mistake is just as common. Hormones are heavily marketed as the hidden explanation for almost any symptom, and direct-to-consumer test kits, "adrenal fatigue" programs and hormone-balancing supplements are widely sold. Genuine hormone disorders are specific and testable, and their treatments carry real risks if taken by people who do not need them. Thyroid hormone taken without a deficiency, for example, can strain the heart and thin the bones.

The practical approach sits between these two extremes. If you have persistent symptoms, ask for appropriate testing, ask for the actual numbers, and make sure results are interpreted in context. If testing is normal, it is worth looking at other common, treatable causes of fatigue and mood change, such as anemia, sleep apnea, depression and medication side effects, rather than continuing to search for a hormonal one.

Underactive thyroid (hypothyroidism)

Hypothyroidism means the thyroid makes too little hormone, slowing many body processes. About 5 in 100 Americans age 12 and older have it, and it is much more common in women and in people over 60. In the US, the most common cause is Hashimoto's disease, an autoimmune condition in which the immune system gradually damages the thyroid. Other causes include previous thyroid surgery or radioactive iodine treatment, some medicines such as lithium and amiodarone, and, less often in the US, iodine deficiency.

Symptoms tend to creep up: tiredness, feeling cold, weight gain, constipation, dry skin, thinning hair, a hoarse voice, heavier or irregular periods, slowed thinking, low mood, and aches in the muscles and joints. Some people notice a swelling in the neck, called a goiter. Because these symptoms are so ordinary, the diagnosis is made with a blood test, typically showing a high TSH with a low free T4.

Treatment is usually levothyroxine, a synthetic form of T4, taken once a day, usually for life. It works well and is inexpensive, but how you take it matters. Take it on an empty stomach, 30 to 60 minutes before breakfast, at the same time each day, with water. Separate it by about 4 hours from iron, calcium, antacids and some other supplements, which block its absorption. Coffee and high-fiber meals taken at the same time can also reduce absorption.

After starting or changing a dose, TSH is usually rechecked in 6 to 8 weeks, because it takes that long for levels to settle. Once you are stable, a yearly check is common. Do not adjust the dose yourself, and tell your doctor about palpitations, tremor, trouble sleeping or weight loss, which can mean the dose is too high. Tell your doctor promptly if you become pregnant, because the dose usually needs increasing straight away.

Subclinical hypothyroidism

Sometimes TSH is mildly raised while free T4 is still normal. This is called subclinical hypothyroidism. It is common, especially in older adults, and often returns to normal on its own, so the usual first step is to repeat the test in a few weeks to months. Whether to treat depends on how high the TSH is, whether you have symptoms or thyroid antibodies, your age, and whether you are pregnant or planning pregnancy. Many people with a mildly raised TSH do not need treatment, only monitoring.

Overactive thyroid (hyperthyroidism)

Hyperthyroidism means the thyroid makes too much hormone, speeding up the body. It affects about 1 in 100 Americans age 12 and older. The most common cause is Graves' disease, an autoimmune condition in which antibodies stimulate the thyroid. Other causes include overactive nodules, temporary inflammation of the thyroid called thyroiditis, which can follow pregnancy or a viral illness, and taking too much thyroid hormone medicine.

Symptoms include weight loss despite a normal or increased appetite, a fast or irregular heartbeat, anxiety and irritability, tremor, sweating and heat intolerance, frequent bowel movements, trouble sleeping, muscle weakness and lighter periods. Older adults may have fewer of these and present mainly with weight loss, tiredness or a new irregular heartbeat. Left untreated, hyperthyroidism raises the risk of atrial fibrillation, heart failure and osteoporosis, so it is not something to ride out.

Treatment options are antithyroid medicine, most often methimazole, radioactive iodine, which shrinks the thyroid over weeks to months, or surgery to remove the thyroid. Each has advantages, and the choice depends on the cause, your age, pregnancy plans, eye involvement and your own preferences. Beta blockers are often used early to control a racing heart and tremor while other treatment takes effect. Radioactive iodine and surgery often lead to hypothyroidism afterward, which is then treated with levothyroxine.

Methimazole and propylthiouracil carry a rare but serious risk: a sudden drop in the white blood cells that fight infection. If you develop a sore throat, mouth sores or a fever while taking either medicine, stop taking it and contact your doctor the same day for an urgent blood count. Propylthiouracil can also, rarely, cause liver injury, so report yellowing of the skin or eyes, dark urine or unusual tiredness. Keep any blood test appointments your doctor arranges while you take these medicines.

Graves' eye disease

Some people with Graves' disease develop thyroid eye disease: gritty, red or watering eyes, puffiness, eyes that seem to bulge, double vision or eye pain. It needs assessment by an eye doctor, and severe forms need urgent treatment to protect vision. Smoking makes thyroid eye disease considerably more likely and more severe, and reduces how well treatment works, so quitting is one of the most useful steps you can take. Radioactive iodine can worsen eye disease in some people, which is one reason it is discussed carefully.

Understanding thyroid tests

TSH is the main screening test. If it is abnormal, free T4 is usually measured, and sometimes T3. A high TSH with a low free T4 points to hypothyroidism; a low TSH with a high free T4 or T3 points to hyperthyroidism. Thyroid antibody tests, such as anti-TPO antibodies, help identify autoimmune thyroid disease and can predict whether a mildly raised TSH is likely to progress. Ask for your actual numbers, not only "normal" or "abnormal."

Several things can distort results. Acute illness, recovery from illness and some medicines, including steroids and high-dose biotin, can push results out of range temporarily, so results taken during a significant illness should usually be repeated once you have recovered. The FDA has warned that biotin, a supplement often taken for hair, skin and nails and sometimes present at high doses in multivitamins, can interfere with many lab tests, including some thyroid tests. Tell your doctor if you take it and ask whether to stop it for a few days before your blood test.

Who should be tested? The US Preventive Services Task Force has found insufficient evidence to recommend routine thyroid screening for adults without symptoms. That is not the same as saying testing is never useful: testing is appropriate if you have symptoms, a goiter, a history of thyroid disease or treatment, other autoimmune conditions such as type 1 diabetes, a strong family history, or if you are pregnant or planning pregnancy and have risk factors. Direct-to-consumer thyroid panels often add little and can lead to unnecessary worry or self-treatment.

Thyroid lumps and thyroid cancer

Thyroid nodules are lumps within the thyroid. They are very common, become more common with age, and are often found by chance on scans done for other reasons. The great majority are benign. Some are fluid-filled cysts, and some produce thyroid hormone on their own. Any new lump you can feel or see in your neck should still be checked, because assessment is how the small number of cancers are found.

Assessment usually involves examination, a TSH blood test and a thyroid ultrasound. The ultrasound describes features such as size, shape, edges and calcium deposits that sort nodules into lower and higher concern. If a nodule looks suspicious and is large enough, a fine needle aspiration biopsy, in which a thin needle takes cells for examination, is usually the next step. It is done in the clinic and takes a few minutes. Many nodules need only follow-up ultrasounds over time.

Most thyroid cancers grow slowly and have an excellent outlook with treatment, which usually involves surgery and sometimes radioactive iodine. Some very small, low-risk cancers may simply be watched. Ultrasound screening of people without symptoms or risk factors is not recommended, because it mainly finds small nodules that would never have caused harm. Risk factors worth mentioning to your doctor include radiation to the head or neck in childhood and a family history of thyroid cancer.

• A lump that is growing quickly
• Hoarseness that does not go away
• Difficulty swallowing or a sense of pressure in the neck
• A hard lump that does not move
• Swollen lymph glands in the neck
• Noisy or difficult breathing, which needs emergency care

Iodine, diet and supplements

Your thyroid needs iodine to make hormone. The recommended dietary allowance for adults is 150 mcg a day, rising to 220 mcg in pregnancy and 290 mcg while breastfeeding. Iodine comes from iodized salt, dairy products, eggs, seafood and seaweed. Most Americans get enough, but people who avoid dairy and seafood, use only non-iodized specialty salts, or follow a vegan diet may get less. Because the extra need in pregnancy is important for the baby's brain development, the American Thyroid Association recommends that people who are pregnant or breastfeeding take a daily supplement containing 150 mcg of iodine, ideally as part of a prenatal vitamin. Not all prenatal vitamins contain iodine, so check the label.

More is not better. The tolerable upper intake level for adults is 1,100 mcg a day, and kelp and other seaweed supplements can contain far more than that, with amounts that vary widely between products. Too much iodine can trigger either an underactive or an overactive thyroid, particularly in people with existing thyroid disease. If you have a thyroid condition, check with your doctor before taking iodine or seaweed supplements.

No diet cures thyroid disease, and claims that specific foods heal Hashimoto's disease are not supported by good evidence. Cruciferous vegetables such as broccoli and cabbage are safe in normal amounts. Supplements sold for "thyroid support" may contain iodine or even actual thyroid hormone without clear labeling, which can be dangerous. Vitamin D, which acts in the body more like a hormone than an ordinary nutrient, also has an upper limit; too much raises blood calcium and can harm the kidneys, so stay within the label dose unless your doctor advises otherwise.

Adrenal glands, cortisol and stress hormones

Your adrenal glands make cortisol, which helps regulate blood pressure, blood sugar, the immune response and your response to stress, as well as aldosterone, which balances salt and water, and epinephrine (also called adrenaline). Cortisol follows a daily rhythm, peaking in the morning. Short-term rises during stress are normal and useful. Despite heavy marketing, "adrenal fatigue" is not a recognized medical diagnosis, and adrenal support supplements have no proven benefit and may contain hormones.

Genuine adrenal disorders are rare but serious. In adrenal insufficiency, including Addison's disease, the glands make too little cortisol, causing fatigue, weight loss, low blood pressure, dizziness on standing, salt craving and sometimes darkening of the skin. It is diagnosed with specific blood tests and treated with daily replacement steroids. In Cushing's syndrome, there is too much cortisol, causing weight gain around the middle and face, thin skin, easy bruising, purple stretch marks, muscle weakness and high blood pressure and blood sugar. The most common cause of Cushing's features is taking prescribed steroid medicines, not a tumor.

If you take steroid tablets for more than a few weeks, your own adrenal glands slow down, and stopping suddenly can cause a dangerous drop in cortisol. Never stop long-term steroids abruptly; your doctor will plan a gradual taper. People with adrenal insufficiency should wear a medical alert ID, carry an emergency steroid injection if prescribed, and follow sick-day rules for raising their dose during illness, as their doctor has instructed. Adrenal crisis, with severe weakness, vomiting, abdominal pain, confusion or collapse, is life-threatening and needs 911.

Reproductive hormones across life

Estrogen, progesterone and testosterone affect far more than fertility, including bones, blood vessels, skin, mood and metabolism. Their levels change across the menstrual cycle, in pregnancy and after childbirth, and at menopause, and these transitions can bring real and treatable symptoms. Mood changes linked to these shifts, such as severe premenstrual mood symptoms, depression during or after pregnancy, and new anxiety or low mood around perimenopause, deserve the same attention as any other mood problem. Hormonal factors can contribute, but they should not be used to explain away depression that needs treating.

Polycystic ovary syndrome (PCOS)

PCOS is one of the most common hormonal conditions, affecting about 6 to 12 percent of US women of reproductive age, and one of the most common causes of irregular periods and infertility. It is usually diagnosed when two of three features are present: irregular or absent ovulation, signs of high androgens such as excess facial or body hair, acne or scalp hair thinning, and polycystic ovaries on ultrasound, after other causes have been ruled out.

PCOS is linked to insulin resistance and a higher risk of type 2 diabetes, high cholesterol and heart disease, so it should be treated as a metabolic condition as well as a reproductive one. Ask for periodic blood glucose and cholesterol checks. Even modest weight loss can help restore ovulation in some people, and treatment options include hormonal birth control, metformin and fertility treatment. Very infrequent periods can let the lining of the uterus thicken, so ask your doctor about protecting it.

Hormonal birth control

Hormonal birth control has benefits beyond preventing pregnancy: combined pills are linked to lower ovarian and endometrial cancer risk, and many methods ease heavy or painful periods. The main serious risk of combined methods, those containing estrogen, is blood clots. US medical eligibility criteria advise against combined methods for people who have migraine with aura, who smoke and are 35 or older, or who have had a blood clot. Progestin-only methods, including implants and hormonal IUDs, suit many people who cannot use estrogen. Long-acting methods are the most effective.

Menopause and hormone therapy

Menopause is confirmed after 12 months without a period, most commonly in the early 50s, and the years of hormonal change before it, perimenopause, can bring hot flashes, night sweats, sleep problems, mood change and irregular bleeding. Menopausal hormone therapy is the most effective treatment for hot flashes and night sweats. For most healthy women under 60 or within 10 years of menopause, guidelines say the benefits generally outweigh the risks.

If you have a uterus, estrogen must be combined with a progestin to protect the uterine lining. Estrogen patches, gels and sprays are linked to a lower clot risk than estrogen pills. Low-dose vaginal estrogen treats vaginal dryness and some urinary symptoms and acts mainly locally. Compounded "bioidentical" hormones are not FDA-approved and have not been tested for safety and consistency in the same way. Review hormone therapy with your doctor yearly, and report any bleeding after menopause, which always needs investigation.

Pregnancy, children, older adults and men

Hormone conditions behave differently at different stages of life, and some groups need particular care with testing and treatment. The notes below cover pregnancy, newborns and children, older adults and men, the groups for whom the general advice in this guide most often needs adjusting. In every case, the safest course is to tell your doctor about any thyroid or hormone condition, and any hormone medicine you take, before planning a change.

Pregnancy and after birth

The baby depends on the mother's thyroid hormone in early pregnancy, and the body's need rises quickly. If you take levothyroxine, tell your doctor as soon as you know you are pregnant, because the dose usually needs to go up promptly, and TSH is checked more often. Antithyroid medicines and radioactive iodine need careful planning around pregnancy, and radioactive iodine is not given during pregnancy or breastfeeding. In the months after birth, some women develop postpartum thyroiditis, which can cause a short overactive phase followed by an underactive one. Depression after childbirth is common and treatable; raise it early.

Newborns and children

Every US state screens newborns for congenital hypothyroidism with the heel-prick blood test, because early treatment prevents serious problems with growth and brain development. In older children, poor growth, delayed or very early puberty, or a neck swelling can point to a hormone problem. Teens with obesity or irregular periods may need checks for PCOS or prediabetes. Your child's doctor will decide what testing is needed.

Older adults and men

TSH tends to drift up slightly with age, so a mildly raised result in an older adult may not need treatment. Older adults on thyroid hormone are more vulnerable to the effects of too high a dose, including atrial fibrillation and bone loss, so the dose is often kept lower. In men, testosterone falls gradually with age. Low testosterone should be confirmed with repeated morning blood tests and assessed by a doctor before any treatment, and testosterone bought without a prescription carries real risks.

Costs, access and common myths

Thyroid care is among the more affordable areas of US medicine. TSH tests are inexpensive and usually covered by insurance when ordered for symptoms or monitoring. Generic levothyroxine is on many low-cost pharmacy price lists, and asking for a 90-day supply can reduce copays. Stay on the same manufacturer's product where possible, or ask for a TSH check after a switch, because small differences between products can matter. If cost is a barrier, ask your pharmacist about discount programs or a cheaper equivalent before skipping doses.

Hormone myths spread easily, partly because the symptoms involved are so common. The list below sets out some of the most persistent beliefs and what current guidance says instead. If you have tried a product or program based on one of them, it is worth telling your doctor, because some contain hormones or iodine that affect test results and treatment.

• Myth: Feeling tired means your thyroid is the problem. Fact: Thyroid disease is one cause among many; a TSH test can quickly check, and other causes are more common.
• Myth: "Adrenal fatigue" explains burnout. Fact: It is not a recognized diagnosis; genuine adrenal disease is rare and testable.
• Myth: Natural thyroid supplements are gentle. Fact: Some contain iodine or thyroid hormone at unpredictable doses, which can cause harm.
• Myth: Hormone therapy for menopause is always dangerous. Fact: For most healthy women under 60 or within 10 years of menopause, benefits generally outweigh risks.
• Myth: You can stop levothyroxine once you feel better. Fact: Most people need it for life; feeling well means it is working.
• Myth: A thyroid lump is probably cancer. Fact: The great majority of nodules are benign, though all should be checked.

Talking to your doctor and a practical plan

Hormone conditions are managed over years, so a good working relationship with your doctor matters. Before an appointment, write down your symptoms, when they started and how they affect your daily life, list every medicine and supplement you take, including biotin, iodine, seaweed and any hormone products, and note your menstrual pattern if relevant. Ask for your results and keep a record so you can see trends over time.

If your symptoms continue despite normal tests or stable treatment, say so clearly rather than adjusting doses yourself. Your doctor can recheck the diagnosis, look for other causes, or refer you to an endocrinologist, a doctor who treats hormone conditions. The questions and four-week plan below are a starting point you can adapt to your own situation, and bringing them to your next appointment makes the time you have with your doctor go further.

• What are my TSH and free T4 numbers, and how do they compare with last time?
• Should thyroid antibodies be checked?
• Is my levothyroxine dose right, and when should it be rechecked?
• Could any of my medicines or supplements be affecting my results?
• If my tests are normal, what else could explain my symptoms?
• Week 1: Write a symptom diary, and list every medicine and supplement, checking labels for biotin and iodine.
• Week 2: Book an appointment and ask whether thyroid or other hormone tests are appropriate for you.
• Week 3: If you take levothyroxine, set a fixed time on an empty stomach, separated from iron and calcium.
• Week 4: Review your birth control, menopause treatment or steroid plan with your doctor if relevant, and if you smoke, ask for help to quit.
• Every year: Check TSH as advised if you are on thyroid treatment, and review any hormone therapy with your doctor.

Every guide in this topic

• What the Guidance Really Says About Underactive Thyroid
• Overactive Thyroid: Sorting the Evidence From the Noise
• What the Guidance Really Says About Thyroid Function Tests
• Thyroid Lumps: What Published Guidance Supports
• The Evidence on Polycystic Ovary Syndrome, Without the Hype
• The Evidence on Hormones and Mood, Without the Hype
• Cortisol and Stress Hormones: What the Evidence Actually Says
• Vitamin D and Hormones: What the Evidence Actually Says
• The Evidence on Hormonal Contraception and Health, Without the Hype
• Hormone Replacement Therapy: Sorting the Evidence From the Noise

Frequently asked questions

What does a high TSH mean?

A high TSH usually means your thyroid is underactive. The pituitary gland raises TSH to push a sluggish thyroid to work harder, so TSH moves in the opposite direction to thyroid hormone. A high TSH with a low free T4 indicates hypothyroidism, while a mildly high TSH with a normal free T4 is called subclinical hypothyroidism and is often rechecked before any treatment.

Can I take levothyroxine with coffee?

It is best not to. Coffee, food, and supplements such as iron and calcium can reduce how much levothyroxine you absorb. Take it with water on an empty stomach, 30 to 60 minutes before breakfast or coffee, at the same time each day. Separate it from iron, calcium and antacids by about 4 hours. If that routine does not suit you, ask your doctor about alternatives.

Can thyroid problems cause weight gain?

An underactive thyroid can cause modest weight gain, much of it from fluid, and an overactive thyroid usually causes weight loss. Once thyroid levels are corrected with treatment, weight often settles somewhat, but thyroid disease rarely explains large weight changes on its own. Taking thyroid hormone to lose weight when your levels are normal is unsafe and can harm the heart and bones.

Is Hashimoto's disease the same as hypothyroidism?

Not exactly. Hashimoto's disease is an autoimmune condition that gradually damages the thyroid, and it is the most common cause of hypothyroidism in the US. Some people with Hashimoto's antibodies still have normal thyroid levels and need only periodic monitoring. When the thyroid can no longer keep up, hypothyroidism develops and is treated with levothyroxine.

Should I stop biotin before a thyroid blood test?

Ask your doctor. The FDA has warned that biotin, especially at the high doses in hair, skin and nail supplements, can interfere with many lab tests and produce falsely high or low results, including some thyroid tests. Many doctors suggest stopping biotin for a few days before blood tests. Always tell your doctor and the lab if you take it.

Do I need an iodine supplement?

Most Americans get enough iodine from iodized salt, dairy, eggs and seafood. The American Thyroid Association recommends a daily supplement containing 150 mcg of iodine during pregnancy and breastfeeding, usually in a prenatal vitamin. Others should generally avoid extra iodine, and kelp or seaweed supplements can contain very high amounts that may upset thyroid function, especially if you already have thyroid disease.

Is adrenal fatigue real?

"Adrenal fatigue" is not a recognized medical diagnosis, and there is no good evidence that stress wears out the adrenal glands. Genuine adrenal insufficiency is rare and can be confirmed with specific blood tests. If you are persistently exhausted, ask your doctor to look for common causes such as thyroid disease, anemia, sleep apnea and depression, and avoid adrenal support supplements, which may contain hormones.

Are thyroid nodules usually cancer?

No. Thyroid nodules are very common and the great majority are benign. Any new neck lump should still be assessed with a TSH test and an ultrasound, and a fine needle biopsy if the ultrasound shows suspicious features. See your doctor promptly for a lump that grows quickly, persistent hoarseness, or difficulty swallowing.

Is hormone therapy for menopause safe?

For most healthy women under 60 or within 10 years of menopause, guidelines say the benefits of hormone therapy for hot flashes and night sweats generally outweigh the risks. Risks depend on your age, health, the type of hormone and how it is taken; patches and gels carry a lower clot risk than pills. Discuss your own situation with your doctor and review it yearly.

What should I do if I get a sore throat on methimazole?

Stop the medicine and contact your doctor the same day for an urgent blood count. A sore throat, mouth sores or fever while taking methimazole or propylthiouracil can be a sign of a rare but dangerous drop in white blood cells, which leaves you unable to fight infection. Do not restart the medicine until your doctor has seen the results.

When to speak to a doctor

See your doctor for persistent tiredness with other changes such as weight change, feeling cold or hot, palpitations or tremor; for any new neck lump; for irregular or very infrequent periods; or for bleeding after menopause. Contact your doctor the same day for a sore throat, mouth sores or fever while taking methimazole or propylthiouracil, for double vision or eye pain with Graves' disease, and promptly if you become pregnant while on thyroid medicine. Call 911 for fever with agitation, a very rapid heart rate and confusion (possible thyroid storm); extreme drowsiness, confusion or very low body temperature; severe weakness, vomiting or collapse in anyone with adrenal insufficiency or on long-term steroids; difficulty breathing; or chest pain, sudden severe headache, one-sided weakness or sudden vision loss on estrogen-containing treatment. For thoughts of suicide, call or text 988.

Where this comes from

• National Institute of Diabetes and Digestive and Kidney Diseases — Hypothyroidism (Underactive Thyroid)
• National Institute of Diabetes and Digestive and Kidney Diseases — Hyperthyroidism (Overactive Thyroid)
• American Thyroid Association — Thyroid Nodules
• US Preventive Services Task Force — Thyroid Dysfunction: Screening
• FDA — The FDA Warns that Biotin May Interfere with Lab Tests
• NIH Office of Dietary Supplements — Iodine Fact Sheet for Health Professionals
• National Institute of Diabetes and Digestive and Kidney Diseases — Adrenal Insufficiency & Addison's Disease
• CDC — Polycystic Ovary Syndrome (PCOS)
• CDC — U.S. Medical Eligibility Criteria for Contraceptive Use, 2024
• American College of Obstetricians and Gynecologists — Hormone Therapy for Menopause

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.