Selenium

Pronunciation: seh-LEE-nee-um.

Generic name
selenium
Drug class
Essential trace mineral / dietary and nutritional supplement (not a prescription drug in most markets)
Form
Tablet, capsule, or liquid drops, typically as selenomethionine (an organic, food-derived form) or sodium selenite/selenate (inorganic forms)
Route
Oral
Legal status
Over-the-counter dietary/nutritional supplement in all markets reviewed -- not an FDA-approved (or equivalent) prescription medicine

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Selenium (generic multi-brand supplement) (5) · Full directory

What selenium is and how it works

Selenium is an essential trace mineral your body needs in small amounts for normal thyroid function, reproduction, DNA production, and protection from oxidative damage and infection. Most people get enough selenium from food (such as Brazil nuts, seafood, meat, and grains) without needing a supplement. (1) (4)

Selenium has a genuinely narrow safe range -- too little can contribute to real, documented deficiency conditions, but too much causes a real toxicity syndrome called selenosis. This is not a risk-free 'more is better' supplement: the gap between a helpful amount and a harmful amount is smaller than for many other vitamins and minerals, and official safe upper limits actually differ between countries (see below), so following your specific product's label and your clinician's or pharmacist's advice matters more than usual.

Mechanism of action: how selenium works

Selenium is incorporated into selenoproteins, including glutathione peroxidases and thioredoxin reductases, which have antioxidant and redox-regulatory roles, and into iodothyronine deiodinases, which are essential for normal thyroid hormone metabolism. This is the biological basis for both its deficiency-related conditions (Keshan disease, thought to involve compromised antioxidant defence in heart muscle, often together with an environmental viral cofactor; Kashin-Beck disease, a joint/bone disorder) and, at excessive intakes, for the toxicity syndrome selenosis. (1) (2)

What selenium is used for

Supporting normal selenium intake when diet alone is insufficient

Used to help meet daily selenium needs in people whose diet does not provide enough, supporting normal thyroid function and antioxidant processes in the body. (1)

Prevention/management of selenium-deficiency-related conditions

In regions or situations of documented severe dietary selenium deficiency, selenium supplementation (often together with iodine) has a real, established role in helping prevent Keshan disease (a heart-muscle condition) and Kashin-Beck disease (a joint and bone condition). (1)

Before taking selenium

Do not take / not appropriate for

  • Do not take a selenium supplement above the amount recommended for your country and age group without your clinician's guidance -- the gap between a normal dose and a harmful one is genuinely narrow for this mineral. (all countries) (1) (4)
  • Do not combine multiple selenium-containing supplements or fortified products without checking the combined total against your country's upper limit -- accidental double-dosing is a real, documented cause of selenosis. (all countries) (1)

Tell your clinician about

  • If you take warfarin or any other blood-thinning (anticoagulant or antiplatelet) medicine.
  • If you take niacin and a statin together for cholesterol.
  • If you are undergoing or have recently had chemotherapy, especially with cisplatin.
  • If you have a thyroid condition or autoimmune disease.
  • If you are pregnant, planning pregnancy, or breastfeeding.
  • If you eat Brazil nuts regularly, since they are naturally very high in selenium and can meaningfully add to your total intake.
(1) (4)

How to take selenium

  • Take exactly the amount stated on your product's label, or as recommended by your clinician or pharmacist, with or without food.
  • Do not exceed your country's recommended upper safe intake -- these figures genuinely differ by country and are all lower than many people assume (see the country-specific figures below).
  • If you are unsure how much selenium you already get from your diet (for example, if you regularly eat Brazil nuts, seafood, or organ meats), discuss this with your clinician before adding a supplement.
(2) (3) (4) (5)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5)

Missed dose

If you miss a daily dose, simply resume your normal schedule at the next planned time. do not take an extra dose to make up for a missed one -- because the safe range is narrow, doubling up raises your risk of exceeding the upper safe intake for your country.

Overdose

Taking a very large amount of selenium at once, or a supplement that turns out to be mislabelled with far more selenium than stated, can cause acute or rapidly developing symptoms (see selenosis warning below). If you suspect an overdose, especially in a child, contact a poison-control service or emergency care immediately rather than waiting to see if symptoms appear. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Mild nausea or an upset stomach, particularly when taken on an empty stomach.

What to notice: Mild nausea or an upset stomach, particularly when taken on an empty stomach.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

A mild, harmless garlic-like odour on the breath can occur even at recommended doses in some people, and is an early warning sign if it becomes noticeably stronger.

What to notice: A mild, harmless garlic-like odour on the breath can occur even at recommended doses in some people, and is an early warning sign if it becomes noticeably stronger.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Selenosis (chronic selenium toxicity) from taking too much for too long — serious

Symptoms: Hair loss, brittle or lost fingernails/toenails, a garlic odour on the breath, a metallic taste in the mouth, skin rash, nausea, diarrhoea, fatigue, irritability, and nervous-system problems. Real documented cases have occurred within about a week of taking a mislabelled supplement containing far more selenium than stated on the label.

Action: Contact your clinician if you notice these symptoms, especially if you take a selenium supplement regularly or eat large amounts of Brazil nuts. Never continue a suspect product -- bring it and its packaging to your clinician or pharmacist rather than guessing at what's in it. (1)

Increased bleeding risk with blood-thinning medicines — high caution

Symptoms: Unusual bruising, prolonged bleeding from small cuts, or blood in stool or urine.

Action: Tell your clinician you are taking a selenium supplement if you are on warfarin or another anticoagulant/antiplatelet medicine -- selenium may have an antiplatelet effect and could increase bleeding risk. (1)

Reduced benefit of niacin-plus-statin cholesterol therapy — high caution

Symptoms: No specific symptom -- this is a reduction in your treatment's effectiveness, which your clinician monitors via cholesterol blood tests.

Action: Tell your clinician about selenium (and other antioxidant) supplement use if you take niacin together with a statin -- combining them may blunt the HDL ('good cholesterol') benefit of that combination therapy. (1)

Possible interaction with cisplatin chemotherapy — high caution

Symptoms: No specific patient-noticeable symptom -- cisplatin can lower selenium levels in the body, though the full clinical significance is not completely clear.

Action: Tell your oncology team about any selenium supplement before or during chemotherapy so they can factor this into your care -- never start, stop, or adjust a supplement during cancer treatment without their guidance. (1)

Interactions

  • Anticoagulant or antiplatelet medicines (e.g. warfarin): selenium may have an antiplatelet effect and could increase bleeding risk when combined. (1)
  • Niacin plus a statin (combination cholesterol therapy): taking selenium and other antioxidants alongside this combination may reduce its HDL-raising benefit. (1)
  • Cisplatin (a chemotherapy drug): can lower selenium levels in the body; the full clinical significance of this interaction is not completely clear, so oncology teams should be informed of selenium supplement use. (1)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

The EU's 2023 EFSA upper intake limit of 255 mcg/day explicitly applies to pregnant women as well as other adults. Selenium is needed for normal fetal development, but exceeding the upper safe intake is not advised during pregnancy any more than at other times. Discuss any supplement use with your clinician or midwife. (1) (2) (3) (4) (5)

Breastfeeding

The same 255 mcg/day EU upper limit explicitly applies to breastfeeding women. Selenium requirements are slightly higher during breastfeeding to support the nutrient content of breast milk, but supplement use should still stay within your country's recommended range and ideally be discussed with your clinician. (1) (2) (3) (4) (5)

Children

Upper safe-intake limits are set separately and are considerably lower for infants and children (for example, 45 mcg/day for infants 0-6 months and 60 mcg/day for infants 7-12 months per the shared US/Canada and Australia/New Zealand references) -- never give a child an adult-strength selenium supplement without a clinician's specific guidance. (1) (2) (3) (4) (5)

Elderly

No specific dose adjustment based on age alone beyond the standard adult RDA/UL figures was identified in the sources reviewed. (1) (2) (3) (4) (5)

Hepatic_impairment

No specific dosing guidance was identified in the sources reviewed for this dossier. (1) (2) (3) (4) (5)

Renal_impairment

No specific dosing guidance was identified in the sources reviewed for this dossier. (1) (2) (3) (4) (5)

Source_ids

US-IOM-DRI-SELENIUM-2026,EU-EFSA-SELENIUM-UL-2023,AU-NZ-NHMRC-SELENIUM-NRV-2026 (1) (2) (3) (4) (5)

Monitoring

Before starting

  • Consider your typical dietary selenium intake (especially Brazil nuts, seafood, organ meats) before adding a supplement
  • Review current medicines for anticoagulants, niacin/statin combination therapy, or ongoing chemotherapy

During treatment

  • Watch for early selenosis warning signs (a stronger-than-usual garlic breath odour or metallic taste) and stop and contact a clinician if these develop.
  • A blood selenium level test can help confirm suspected toxicity or deficiency if your clinician recommends one (levels above roughly 100 mcg/dL can indicate selenosis).
  • If on anticoagulants, watch for unusual bruising or bleeding and report it promptly.
(1)

Storage

Store at room temperature, away from moisture and direct light, out of reach of children, following the instructions on your specific product's label.

Professional information

Clinician-facing context only, sourced from the NIH Office of Dietary Supplements Health Professional Fact Sheet, the shared US/Canada Institute of Medicine DRI report, UK NHS/SACN guidance, the EU's 2023 EFSA opinion, and Australia/New Zealand's joint NHMRC NRV; verify against current national nutrient guidance, which is genuinely still evolving for this nutrient.

United States / Canada

Indication: General nutrient adequacy / deficiency prevention

Dose summary: RDA 55 mcg/day (adults); UL 400 mcg/day (adults), based on preventing selenosis.

Renal context: No specific renal dosing guidance identified in the sources reviewed. (2)

European Union

Indication: General nutrient adequacy / deficiency prevention

Dose summary: UL 255 mcg/day (adults, including pregnancy/lactation) per EFSA 2023, a genuine downward revision from an earlier ~300 mcg/day figure.

Renal context: No specific renal dosing guidance identified in the sources reviewed. (4)

United Kingdom

Indication: General nutrient adequacy / deficiency prevention

Dose summary: RNI 75 mcg/day (men), 60 mcg/day (women); NHS guidance: supplement intake up to 350 mcg/day unlikely to cause harm.

Renal context: No specific renal dosing guidance identified in the sources reviewed. (3)

Australia / New Zealand

Indication: General nutrient adequacy / deficiency prevention

Dose summary: Current UL 400 mcg/day (adults, 2006 NRV), under active public-consultation review as of early 2026 and may be lowered.

Renal context: No specific renal dosing guidance identified in the sources reviewed. (5)

Mechanism of action

Hepatic guidance

No specific hepatic dosing guidance identified in the sources reviewed.

Overdose note

Acute or chronic selenium overdose (selenosis) is managed by discontinuation of the supplement/source and supportive care; documented case reports show symptoms including hair/nail loss, gastrointestinal upset, and neurological symptoms developing within about a week of high-dose exposure. (1) (2)

Frequently asked questions

Is more selenium always better?

No. Selenium has a genuinely narrow safe range -- both too little and too much cause real health problems. Too little contributes to documented deficiency conditions (Keshan disease, Kashin-Beck disease), while too much causes a toxicity syndrome called selenosis, with symptoms including hair loss, brittle nails, a garlic breath odour, and gastrointestinal and nervous-system problems. Always stay within your country's recommended range rather than assuming a higher dose is automatically more beneficial. (1)

Why do different countries recommend different maximum amounts of selenium?

Regulators in different countries have reviewed similar underlying safety evidence but reached somewhat different conclusions and review timelines: the US/Canada Tolerable Upper Intake Level is 400 mcg/day, the UK's NHS states up to 350 mcg/day is unlikely to cause harm, the EU's 2023 EFSA opinion set a lower 255 mcg/day limit, and Australia/New Zealand's current 400 mcg/day figure is under active review and may be lowered. This reflects genuinely evolving nutritional science, not an error in any one country's guidance. (2) (3) (4) (5)

Can I take selenium if I'm on blood thinners or chemotherapy?

Tell your clinician before doing so. Selenium may increase bleeding risk when combined with anticoagulant or antiplatelet medicines like warfarin, and it can interact with certain chemotherapy drugs such as cisplatin. Never start or continue a selenium supplement during these treatments without your clinician's or oncology team's specific guidance. (1)

Do Brazil nuts count toward my selenium intake?

Yes, and significantly so -- Brazil nuts are naturally very high in selenium, and regularly eating them alongside a supplement is a real, documented way people accidentally exceed the safe upper intake. Factor your typical diet in before adding a supplement. (4)

What is the mechanism of action of selenium?

Selenium is incorporated into selenoproteins, including glutathione peroxidases and thioredoxin reductases, which have antioxidant and redox-regulatory roles, and into iodothyronine deiodinases, which are essential for normal thyroid hormone metabolism. This is the biological basis for both its deficiency-related conditions (Keshan disease, thought to involve compromised antioxidant defence in heart muscle, often together with an environmental viral cofactor; Kashin-Beck disease, a joint/bone disorder) and, at excessive intakes, for the toxicity syndrome selenosis. (1) (2)

What is the generic name of Selenium?

The generic name is selenium. (1) (2)

What class of drug is selenium?

Selenium is classed as: Essential trace mineral / dietary and nutritional supplement (not a prescription drug in most markets). (1) (2)

References

  1. Selenium -- Health Professional Fact SheetNational Institutes of Health, Office of Dietary Supplements (ODS) -- Health Professional Fact Sheet · United States · accessed 2026-07-30 · source 1
  2. Selenium -- Dietary Reference Intakes (DRI) reportInstitute of Medicine (US National Academies) / Health Canada -- Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (shared US/Canada reference) · United States, Canada · accessed 2026-07-30 · source 2
  3. NHS selenium supplement guidance; SACN Position Statement on Selenium and Health (2013)NHS (UK National Health Service) and the Scientific Advisory Committee on Nutrition (SACN) · United Kingdom · accessed 2026-07-30 · source 3
  4. Scientific opinion on the tolerable upper intake level for selenium (EFSA Journal, 2023)European Food Safety Authority (EFSA) -- Scientific Opinion on the Tolerable Upper Intake Level for Selenium · European Union · accessed 2026-07-30 · source 4
  5. Nutrient Reference Values for Australia and New Zealand -- Selenium (2006, currently under public-consultation review)National Health and Medical Research Council (NHMRC), Australia, and New Zealand Ministry of Health -- joint Nutrient Reference Values for Australia and New Zealand · Australia, New Zealand · accessed 2026-07-30 · source 5

Brand names by country

Single-ingredient selenium names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Selenious Acid6 ug/mL, 60 ug/mL, 40 ug/mL · american regent, inc.
  • Selenium metallicum1 [hp_M], 6 [hp_C], 500 [hp_C], 1 [hp_Q], 12 [hp_C]2[hp_C], 30 [hp_C]/30[hp_C], 100 [hp_C], 200 [kp_C]/200[kp_C] · hahnemann laboratories, inc.
  • Bestmade Natural Products Selenium6 [hp_X]/6[hp_X], 30 [hp_C]/30[hp_C] · bestmade natural products
  • Black gold16 mg · zhongbaokang biotechnology co., ltd
  • BM Selenium (Selenium)6 [hp_X]/60mg · bm private limited

United Kingdom

  • Selenium (generic multi-brand supplement) (3)recognised dietary supplement ingredient NHS SACN guidance · typically 50-200 mcg per tablet/capsule · Various generic supplement manufacturers

Canada

  • MICRO SE

Australia

  • Selenium (generic multi-brand supplement) (5)recognised dietary supplement ingredient NHMRC NRV guidance · typically 50-200 mcg per tablet/capsule · Various generic supplement manufacturers

New Zealand

  • Selenium (generic multi-brand supplement) (5)recognised dietary supplement ingredient joint NRV guidance · typically 50-200 mcg per tablet/capsule · Various generic supplement manufacturers
View brands in additional countries.

European Union

Selenium (generic multi-brand supplement) (4)

This page provides general reference information about selenium and is not a substitute for advice from a clinician, pharmacist, or dietitian. Recommended and upper safe intake amounts genuinely differ by country and personal circumstances -- always check your specific product's label and seek professional advice before starting, stopping, or combining supplements.

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