Selenium (Selenomethionine)

Organic selenium form with superior bioavailability and storage capacity for long-term selenium status

Scientific nameL-Selenomethionine FormulaC5H11NO2Se Molecular weight196.11 g/mol CAS3211-76-5

95 absorption score

7 safety / 10

15 USD per month

40 elemental selenium %

5 documented interactions

Check it against something

Evidence level A

Selenium (Selenomethionine) with:

99 out of 100

Works better together Compatible. Timing differs, so follow each supplement's own window.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Superior bioavailability and retention

Better absorbed and stored than inorganic selenium forms

Organic form incorporated into proteins for long-term storage Evidence A-grade 2-4 weeks

Enhanced antioxidant protection

Powerful antioxidant enzyme support and free radical protection

Essential cofactor for glutathione peroxidase and other enzymes Evidence A-grade 4-8 weeks

Optimal thyroid function

Critical for thyroid hormone metabolism and function

Required for deiodinase enzymes that activate thyroid hormones Evidence A-grade 4-12 weeks

Immune system support

Enhances immune response and infection resistance

Essential for immune cell function and antibody production Evidence A-grade 4-8 weeks

Cancer prevention potential

May reduce risk of certain cancers

Antioxidant protection and DNA repair support Evidence B-grade Months to years

Others take these for the same thing

Same goal, different mechanism — check any of them against this one

Melatonin Sleep support & circadian rhythm 0.5-3mg A 50% Turmeric Anti-inflammatory & antioxidant 300-1000mg A 3% Glutathione Master antioxidant & detox support 250-750mg B 20% Astaxanthin Superior antioxidant & skin protection 4-12mg B 20% Boron - Essential Trace Mineral for Bone and Hormone Health Bone health & hormone support 3-10mg daily B 85% SAM-e Mood support & liver health 400-800mg A 70%

Every pair we checked

12 combinations scored by the engine

Selenium (Selenomethionine) + Caffeine No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Creatine Monohydrate No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Calcium Carbonate No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Whey Protein No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Lactase No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Bovine Collagen No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + DHA No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Turmeric No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Fish Oil (EPA/DHA) No documented interaction either way No known interaction 70

Selenium (Selenomethionine) + Vitamin D3 Both work together in antioxidant protection Works better together 90

Selenium (Selenomethionine) + Vitamin C (Ascorbic Acid) Both work together in antioxidant protection Works better together 90

Selenium (Selenomethionine) + Iodine (Thyroid Support) Both essential for optimal thyroid function Works better together 94

Dosage

With food

Daily100-200 mcg

Maintenance55-100 mcg

Therapeutic100-200 mcg

Upper limit400 mcg daily

Toxic threshold>800 mcg daily

Upper limit 400 mcg NIH ODS

Before you take it

VeganYes

When to expect it

First Effects2-4 weeks for antioxidant and immune benefits

Peak Benefits8-16 weeks for thyroid and comprehensive benefits

Deficiency DevelopmentMonths to years in selenium-poor areas

Toxicity OnsetWeeks to months with excessive intake

How to measure it

$60-120

MarkerSerum selenium or whole blood selenium

Optimal70-150 ng/mL (0.89-1.9 μmol/L)

Deficient below<70 ng/mL (<0.89 μmol/L)

FrequencyEvery 6-12 months if supplementing regularly

What people actually reported to the FDA

CAERS, 63 reports naming it as the suspect

Most reported effects

Nausea 8

Dizziness 7

Fatigue 6

Vomiting 6

Pain 5

Named as the suspect 63 reports of 151 that mention it at all

Serious outcome 77% hospitalisation, emergency room or worse

Other Serious or Important Medical Event43

Visited a Health Care Provider27

Hospitalization23

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not

Elemental selenium 40.3% of 196.11 g/mol

Absorption Very high 95 of 100 · best absorbed form of this compound

Delivered daily 0.1 mg

Cost per 1 mg delivered $8.71 comparative — uses the absorption score, not a measured percentage

A 500 mg capsule of Selenium (Selenomethionine) contains 202 mg of selenium. How much of that crosses into your blood is not measured for this form — the absorption score ranks it against other forms, it is not a share of the dose. How this is calculated →

Works better with

3 documented

Vitamin E

Both work together in antioxidant protection

Complementary roles in preventing lipid peroxidation · level A

Vitamin C

Both support antioxidant enzyme systems

Complementary antioxidant protection mechanisms · level B

Iodine

Both essential for optimal thyroid function

Selenium required for thyroid hormone metabolism · level A

What not to take with Selenium (Selenomethionine)

2 documented

Mercury

Mercury depletes selenium and vice versa

Formation of inactive mercury-selenium complexes · major significance

Vitamin C Megadose

Very high vitamin C may reduce selenium absorption

Potential interference with selenium uptake · mild significance

Medication interactions

Discuss these with a pharmacist before combining

warfarin-anticoagulants Minor

May enhance anticoagulant effects

What to do: Monitor clotting times if using high doses

cisplatin-chemotherapy Potentially beneficial

May reduce chemotherapy toxicity

What to do: Consult oncologist about timing

statins Beneficial

May reduce statin-induced muscle damage

What to do: Consider selenium supplementation

Available forms

bioavailability compared

Best absorbed form of Selenium — 95% against 1 alternatives. Compare all forms →

L-Selenomethionine 95

L-Selenomethionine: Superior bioavailability, Long-term storage, Natural form, Better retention

Food sources

before you supplement

Brazil nuts 95-190 mcg per nut · 90

Seafood (tuna, salmon) 40-65 mcg per 100g · 85

Organ meats 15-40 mcg per 100g · 80

Whole grains (varies by soil) 5-40 mcg per serving · 60

Too little

deficiency signs

Muscle weakness and fatigue
Thyroid dysfunction
Increased infection susceptibility
Hair loss and nail changes
Fertility problems
Keshan disease (severe deficiency)
Increased cancer risk

Too much

toxicity signs

Selenosis: garlic breath and metallic taste
Hair loss and brittle nails
Skin rash and dermatitis
Nervous system abnormalities
Nausea and digestive upset
Fatigue and irritability

Who benefits most

thyroid-disorders

Essential for optimal thyroid hormone metabolism

100-200 mcg daily

antioxidant-support-aging

Superior antioxidant enzyme support for healthy aging

100-200 mcg daily

immune-system-support

Critical for optimal immune function

100-200 mcg daily

cancer-prevention-focused

Potential protective effects against certain cancers

100-200 mcg daily

selenium-deficient-regions

Essential for those in low-selenium soil areas

100-200 mcg daily

Where to buy it

compare forms first

Look for Selenium (Selenomethionine) at 100-200 mcg per serving. The form that matters here is L-Selenomethionine.

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How it works

Essential cofactor for glutathione peroxidase antioxidant enzymes
Required for thioredoxin reductase and other selenoproteins
Critical for thyroid hormone deiodinase enzymes
Involved in DNA synthesis and repair
Essential for sperm production and fertility
Supports immune cell function and development

Key findings

what the evidence supports

Essential for thyroid hormone metabolism (established science)
Superior bioavailability and retention vs inorganic forms
Critical antioxidant enzyme cofactor (glutathione peroxidase)
May reduce cancer risk in selenium-deficient populations

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of Selenium (Selenomethionine)?

Documented effects: Superior bioavailability and retention; Enhanced antioxidant protection; Optimal thyroid function; Immune system support. Better absorbed and stored than inorganic selenium forms

How much Selenium (Selenomethionine) should you take per day?

The common daily range is 100-200 mcg. By goal — maintenance: 55-100 mcg; therapeutic: 100-200 mcg; upper limit: 400 mcg daily; toxic threshold: >800 mcg daily.

When is the best time to take Selenium (Selenomethionine)?

With food. First effects are typically reported within 2-4 weeks for antioxidant and immune benefits.

What are the side effects of Selenium (Selenomethionine)?

At excessive doses: Selenosis: garlic breath and metallic taste, Hair loss and brittle nails, Skin rash and dermatitis, Nervous system abnormalities, Nausea and digestive upset. Safety rating at normal doses is 7 out of 10.

What should you not take with Selenium (Selenomethionine)?

Separate it from Mercury, Vitamin C Megadose by two to four hours. Mercury depletes selenium and vice versa

Does Selenium (Selenomethionine) interact with medications?

Documented interactions with warfarin-anticoagulants, cisplatin-chemotherapy, statins. Discuss these with a pharmacist before combining.

How much Selenium (Selenomethionine) is too much?

The tolerable upper intake level is 400 mcg per day for adults, per NIH ODS. Above that, the risk of adverse effects rises: Selenosis: garlic breath and metallic taste, Hair loss and brittle nails, Skin rash and dermatitis.

How do you know if you need Selenium (Selenomethionine)?

The marker is Serum selenium or whole blood selenium, optimal range 70-150 ng/mL (0.89-1.9 μmol/L). Common deficiency signs: Muscle weakness and fatigue, Thyroid dysfunction, Increased infection susceptibility, Hair loss and nail changes.

Taken for

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27 Hormones

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