Herb & supplement monograph

Selenium Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Selenium interacts with medications. The heart of this page is the interaction list — every drug Selenium is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Selenium is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Selenium Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Selenium drug interaction appears low for most people. None of the listed interactions are rated major, and nearly all rest on lab, animal, or early-stage research rather than well-documented effects in humans.

Interactions deserving the most attention

The combinations that deserve the most care involve warfarin and other anticoagulant or antiplatelet drugs, since some human research suggests selenium can lengthen bleeding time. Selenium may also stimulate the immune system, which could theoretically work against immunosuppressants, a meaningful concern for transplant patients whose medicines are closely monitored. Animal research also hints selenium could prolong the sedating effect of barbiturates, though this has not been shown in people.

What the rest of the list means

Selenium appears alongside a long list of medications, but a big number does not mean every pairing is harmful. Most of these interactions are theoretical, based on possible effects on how the body clears certain medications or on immune activity. Where human data exists, such as with contraceptives or niacin, the effects were modest, conflicting, or of unclear real-world importance.

Check your medications against Selenium

Based on HelloPharmacist’s Selenium interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Selenium

321 medications have a known interaction with Selenium, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Selenium using our pharmacist-reviewed interaction data.

AI summaries are generated from our Selenium interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Selenium combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Selenium affects

Every type of medication (drug category) Selenium is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 6 drug categories Selenium interacts with

Anticoagulant/antiplatelet DrugsBarbituratesImmunosuppressantsWarfarin (coumadin)Contraceptive DrugsNiacin

Anticoagulant/Antiplatelet Drugs

Selenium may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Clinical research suggests that taking selenium 10 mcg/kg/day can increase bleeding times by increasing prostacyclin production, which inhibits platelet activity. Other clinical research suggests that taking selenium 75 mcg daily, in combination with ascorbic acid 600 mg, alpha-tocopherol 300 mg, and beta-carotene 27 mg, reduces platelet aggregation.

Likelihood Possible Evidence D

Barbiturates

Theoretically, selenium might prolong the sedating effects of barbiturates.
Laboratory research suggests that selenium can inhibit the hepatic metabolism of barbiturates. Selenium seems to prolong the sedative effect of pentobarbital in animal models.

Likelihood Possible Evidence D

Immunosuppressants

Theoretically, selenium supplementation may reduce the effectiveness of immunosuppressant therapy.
In vitro research and preliminary clinical evidence suggests that selenium may stimulate the immune system.

Likelihood Possible Evidence D

Warfarin (Coumadin)

Theoretically, selenium might interfere with warfarin activity.
Animal research suggests that selenium can increase warfarin activity. Selenium might interact with warfarin by displacing it from albumin binding sites, reducing its metabolism in the liver, or by decreasing production of vitamin K-dependent clotting factors. Selenium can also prolong bleeding times in humans by increasing prostacyclin production, which inhibits platelet activity.

Likelihood Possible Evidence D

Contraceptive Drugs

Contraceptive drugs might increase levels of selenium, although the clinical significance of this effect is unclear.
Some research suggests that oral contraceptives increase serum selenium levels in women taking oral contraceptives; however, other research shows no change in selenium levels. It is suggested that an increase could be due to increased carrier proteins, indicating a redistribution of selenium rather than a change in total body selenium.

Likelihood Possible Evidence B

Niacin

Selenium might reduce the beneficial effects of niacin on high-density lipoprotein (HDL) levels.
A combination of niacin and simvastatin (Zocor) effectively raises HDL cholesterol levels in patients with coronary disease and low HDL levels. Clinical research shows that taking a combination of antioxidants (vitamin C, vitamin E, beta-carotene, and selenium) along with niacin and simvastatin (Zocor) attenuates this rise in HDL, specifically the HDL-2 and apolipoprotein A1 fractions, by more than 50% in patients with coronary disease. It is not known whether this adverse effect is due to a single antioxidant such as selenium, or to the combination. It also is not known whether it will occur in other patient populations.

Likelihood Possible Evidence A

Monograph

Selenium: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Selenium is an essential trace mineral your body needs in small amounts for thyroid function, antioxidant defense, and immune health. Most people who eat a varied diet get enough, and supplements are mainly useful for those who are deficient. Because too much selenium can be toxic, stick to recommended amounts and check with your pharmacist or doctor before supplementing.

Part used: Not applicable (selenium is a mineral, not a plant)
Common forms: Tablets, capsules, softgels, multivitamin/mineral products; common forms include selenomethionine, sodium selenite, and selenium-enriched yeast

People commonly use it for

Thyroid health support
Antioxidant support
Immune support
General nutrient supplementation
Reproductive/fertility support

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Safe in small recommended amounts, but excess selenium can be toxic.

PregnancyPossibly Safe

When used orally and appropriately. Selenium appears to be safe when used short-term in amounts that do not exceed the tolerable upper intake level (U...

Read the full pregnancy detail

BreastfeedingPossibly Safe

When used orally and appropriately. Selenium appears to be safe when used short-term in amounts that do not exceed the tolerable upper intake level (U...

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Selenium is an essential trace mineral, which means your body needs only a small amount but cannot function properly without it. Unlike herbs, it is not made from a plant. It is found naturally in soil and water, and it makes its way into our diet through foods grown in that soil.

Good dietary sources include Brazil nuts, seafood, organ meats, eggs, poultry, and whole grains. The amount of selenium in plant foods depends a lot on how much selenium is in the soil where they grew, so levels vary from region to region.

People take selenium supplements to make sure they get enough, to support thyroid and immune health, and for its antioxidant properties. Most people who eat a balanced diet already get the selenium they need.

How it works

Selenium is used by the body to build special proteins called selenoproteins. Many of these act as antioxidant enzymes (such as glutathione peroxidases) that help protect cells from damage caused by unstable molecules called free radicals.

Selenium is also needed to make enzymes (deiodinases) that help convert thyroid hormone into its active form. This is why it plays an important role in thyroid function.

It also supports the normal working of the immune system. Much of the detailed mechanism comes from laboratory and animal research, and having more selenium than your body needs does not make these systems work better.

Effectiveness

Does Selenium work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 77 uses evaluated

1 Likely effective 3 Possibly effective 13 Leans ineffective 60 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Likely Effective Selenium deficiency