Drug & supplement interaction

Selenium + Peginterferon alfa-2a

Peginterferon alfa-2a brand name: Pegasys IV.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Selenium and Peginterferon alfa-2a in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Selenium and Peginterferon alfa-2a

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Peginterferon alfa-2a and Selenium in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Selenium safety at a glance

Selenium overall Use caution Safe in small recommended amounts, but excess selenium can be toxic.
Pregnancy Possibly 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 (UL) of 400... Read the full pregnancy detail
Breastfeeding Possibly 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 (UL) of 400... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Peginterferon alfa-2a and Selenium? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
Keep it in perspective

Selenium Does Interact With Other Medications

Selenium has 288 moderate, 33 minor known drug interactions in our database — Peginterferon alfa-2a isn’t one of them. If you take anything else, check it against the full list below.

Moderate 288 Minor 33 No known interaction 2,509 (incl. Peginterferon alfa-2a)
Taking anything else?

Check Another of Your Medications Against Selenium

Covers the 2,830 medications we’ve checked against Selenium. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Selenium and Peginterferon alfa-2a May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do. 2 of them are worth acting on rather than waiting out — marked below.

  • A change in thyroid levels / High blood sugar Worth acting on Additional detail

    Selenium

    “Multiple clinical studies have found an association between increased intake of selenium, either in the diet or as a supplement, and the risk for type 2 diabetes. One meta-analysis shows that a selenium plasma level of 90 mcg/L or 140 mcg/L is associated with a 50% or 260% increased risk for developing type 2 diabetes, respectively, when compared with plasma levels below 90 mcg/L.”

    Selenium · Natural Medicines adverse-effect record, reported in diabetes.

    5 sources cited
    1. 97091. Thompson PA, Ashbeck EL, Roe DJ, et al. Selenium Supplementation for Prevention of Colorectal Adenomas and Risk of Associated Type 2 Diabetes. J Natl Cancer Inst. 2016;108(12). PubMed
    2. 99661. Vinceti M, Filippini T, Rothman KJ. Selenium exposure and the risk of type 2 diabetes: a systematic review and meta-analysis. Eur J Epidemiol. 2018 Sep;33(9):789-810. Epub 2018 Jul 5. Review. PubMed
    3. 14563. Contempre B, Dumont JE, Ngo B, et al. Effect of selenium supplementation in hypothyroid subjects of an iodine and selenium deficient area: the possible danger of indiscriminate supplementation of iodine-deficient subjects with selenium. J Clin Endocrinol PubMed
    4. 14565. Hofbauer LC, Spitzweg C, Magerstadt RA, Heufelder AE. Selenium-induced thyroid dysfunction. Postgrad Med J 1997;73:103-4. PubMed
    5. 16707. Lippmann SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the selenium and vitamin E cancer prevention trial (SELECT). JAMA 2009;301:39-51. DOI

    Peginterferon alfa-2a

    Listed in the ADVERSE REACTIONS section of the FDA label for Peginterferon alfa-2a. Read the label on DailyMed ›

  • Hair loss / Tiredness Additional detail

    Selenium

    “Orally, selenium is generally well-tolerated when used in doses that do not exceed the tolerable upper intake level (UL) of 400 mcg daily. Intravenously, selenium is generally well-tolerated.

    Most Common Adverse Effects:

    Orally: Gastric discomfort, headache, and rash.”

    Selenium · Natural Medicines adverse-effect record, reported in alopecia.

    Peginterferon alfa-2a

    Listed in the ADVERSE REACTIONS section of the FDA label for Peginterferon alfa-2a. Read the label on DailyMed ›

  • Joint pain / Muscle pain Additional detail

    Selenium

    “Chronic selenium exposure of 30 mg daily for up to 24 weeks may cause arthralgia, myalgia, and muscle spasms.”

    Selenium · Natural Medicines adverse-effect record, reported in myalgia.

    1 source cited
    1. 113660. Malpas CB, Vivash L, Genc S, et al. A Phase IIa Randomized Control Trial of VEL015 (Sodium Selenate) in Mild-Moderate Alzheimer's Disease. J Alzheimers Dis. 2016;54(1):223-232. PubMed

    Peginterferon alfa-2a

    Listed in the ADVERSE REACTIONS section of the FDA label for Peginterferon alfa-2a. Read the label on DailyMed ›

  • Vomiting / Nausea Additional detail

    Selenium

    “In human research, nausea, vomiting, and liver dysfunction has been reported as a result of high selenium exposure. Mild gastric discomfort has been reported in patients taking up to 200 mcg of selenium daily for up to 12 months.”

    Selenium · Natural Medicines adverse-effect record, reported in nausea and vomiting.

    4 sources cited
    1. 74439. Kamble, P., Mohsin, N., Jha, A., Date, A., Upadhaya, A., Mohammad, E., Khalil, M., Pakkyara, A., and Budruddin, M. Selenium intoxication with selenite broth resulting in acute renal failure and severe gastritis. Saudi.J Kidney Dis.Transpl. 2009;20(1):106
    2. 74376. Spiller, H. A. and Pfiefer, E. Two fatal cases of selenium toxicity. Forensic Sci Int 8-24-2007;171(1):67-72. PubMed
    3. 113660. Malpas CB, Vivash L, Genc S, et al. A Phase IIa Randomized Control Trial of VEL015 (Sodium Selenate) in Mild-Moderate Alzheimer's Disease. J Alzheimers Dis. 2016;54(1):223-232. PubMed
    4. 97943. Wichman J, Winther KH, Bonnema SJ, Hegedüs L. Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid 2016;26(12):1681-92. PubMed

    Peginterferon alfa-2a

    Listed in the ADVERSE REACTIONS section of the FDA label for Peginterferon alfa-2a. Read the label on DailyMed ›

  • Headache Additional detail

    Selenium

    “Chronic exposure to organic and inorganic selenium may cause neurotoxicity, particularly motor neuron degeneration, leading to an increased risk of amyotrophic lateral sclerosis (ALS). Headache has been reported in patients taking up to 200 mcg of selenium daily for up to 12 months and in patients taking sodium selenate 30 mg daily for up to 24 weeks.”

    Selenium · Natural Medicines adverse-effect record, reported in amyotrophic lateral sclerosis (als, lou gehrig's disease).

    3 sources cited
    1. 74304. Vinceti, M., Wei, E. T., Malagoli, C., Bergomi, M., and Vivoli, G. Adverse health effects of selenium in humans. Rev.Environ.Health 2001;16(4):233-251. PubMed
    2. 97943. Wichman J, Winther KH, Bonnema SJ, Hegedüs L. Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid 2016;26(12):1681-92. PubMed
    3. 113660. Malpas CB, Vivash L, Genc S, et al. A Phase IIa Randomized Control Trial of VEL015 (Sodium Selenate) in Mild-Moderate Alzheimer's Disease. J Alzheimers Dis. 2016;54(1):223-232. PubMed

    Peginterferon alfa-2a

    Listed in the ADVERSE REACTIONS section of the FDA label for Peginterferon alfa-2a. Read the label on DailyMed ›

Reported for Selenium but not commonly for Peginterferon alfa-2a: weight loss and a skin rash.

Effects for Peginterferon alfa-2a come from the ADVERSE REACTIONS section of its FDA label; effects for Selenium come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Selenium in Pregnancy & Breastfeeding

Pregnancy Possibly 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 (UL) of 400 mcg daily; however, there is concern that long-term use might not be safe.

Pregnancy Possibly Unsafe

When used orally in excessive doses. Doses above 400 mcg daily may cause significant toxicity.

Lactation Possibly 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 (UL) of 400 mcg daily when taken short-term; however, there is concern that long-term use might not be safe.

Lactation Possibly Unsafe

When used orally in excessive doses. Doses above 400 mcg daily may cause significant toxicity. ...when used orally in HIV-positive women. Selenium supplementation in HIV-positive women not taking highly active antiretroviral therapy may increase HIV-1 levels in breast milk.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

From our Q&A

Questions About Selenium or Peginterferon alfa-2a

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Selenium or Peginterferon alfa-2a, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

One more smart check

Taking Selenium as Part of a Dietary Supplement Product? Check It for Interactions

We hold 16,942 real supplement products containing Selenium, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Selenium. Even though Selenium itself has no known interaction with Peginterferon alfa-2a, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Selenium and Peginterferon alfa-2a Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Selenium
Top 1%

#15 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Peginterferon alfa-2a
Top half

#834 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Selenium reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Selenium and Peginterferon alfa-2a records this page draws on were last updated July 11, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Selenium

What is Selenium?

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

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.

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

An interaction check asks whether these two react with each other — it does not ask whether Selenium is a good idea for someone in your situation. Here is what our Selenium record says about it on its own.

Selenium: dosing

Selenium needs are usually measured in micrograms (mcg) per day, and recommended amounts differ by age and life stage. Most adults need only a small daily amount, which many people already get from food. Health authorities also set an upper limit for safe daily intake that should not be exceeded.Because the right amount depends on your diet, health, and whether you are actually deficient, there is no single dose that fits everyone. Follow the product label and avoid stacking multiple products that all contain selenium.

From our Selenium monograph — the full record covers uses, side effects and every documented interaction.

Read the full Selenium monograph & all interactions
Medication

About Peginterferon Alfa-2a Injection

What Is Peginterferon Alfa-2a Injection Used For?

Brand name: Pegasys IV

Pegasys (peginterferon alfa-2a) is used to treat chronic hepatitis C (CHC) and chronic hepatitis B (CHB). For chronic hepatitis C in adults, Pegasys is typically used in combination with other hepatitis C antiviral drugs; it may be used alone only if other HCV drugs cannot be tolerated or are contraindicated. For children aged 5 and older with CHC, Pegasys is used in combination with ribavirin.

For chronic hepatitis B, Pegasys treats adults who have HBeAg-positive or HBeAg-negative CHB with compensated liver disease and evidence of active viral replication and liver inflammation. In children aged 3 and older with HBeAg-positive CHB (without cirrhosis), Pegasys is also indicated when there is evidence of viral replication and liver enzyme elevation.

See full Peginterferon Alfa-2a Injection drug information
Keep checking

Other Drugs & Selenium

Browse every other medication we’ve checked against Selenium — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
288Moderate
33Minor
2,508No known interaction
288 Moderate 33 Minor 2,508 No interaction
Moderate

288 interactions

Showing 60 of 288 moderate interactions — see all 288 on the Selenium page.

Minor

33 interactions

No interaction 2,508 drugs checked — show the list

We also checked Selenium against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,508 medications checked with no known interaction — see the full Selenium list.

See the full Selenium interactions page
See every supplement checked against Peginterferon alfa-2a, ranked by severity
Evidence & sources

Selenium References

The 36 references that drive our Selenium monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academy Press, 2000. Available at: http://www.nap.edu/books/0309069351/html/.
  2. Brown BG, Zhao XQ, Chait A, et al. Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease. N Engl J Med 2001;345:1583-93. DOI
  3. Trafikowska U, Zachara BA, Wiacek M, et al. Selenium supply and glutathione peroxidase activity in breastfed Polish infants. Acta Paediatr 1996;85:1143-5. PubMed
  4. Duffield-Lillico AJ, Slate EH, Reid ME, et al. Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. J Natl Cancer Inst 2003;95:1477-81.. PubMed
  5. Cheung MC, Zhao XQ, Chait A, et al. Antioxidant supplements block the response of HDL to simvastatin-niacin therapy in patients with coronary artery disease and low HDL. Arterioscler Thromb Vasc Biol 2001;21:1320-6. PubMed
  6. Schiavon R, Freeman GE, Guidi GC, et al. Selenium enhances prostacyclin production by cultured endothelial cells: possible explanation for increased bleeding times in volunteers taking selenium as a dietary supplement. Thromb Res 1984;34:389-96. PubMed
  7. Davila JC, Edds GT, Osuna O, Simpson CF. Modification of the effects of aflatoxin B1 and warfarin in young pigs given selenium. Am J Vet Res 1983;44:1877-83. DOI
  8. Heese HD, Lawrence MA, Dempster WS, Pocock F. Reference concentrations of serum selenium and manganese in healthy nulliparas. S Afr Med J 1988;73:163-5.
  9. Lloyd B, Lloyd RS, Clayton BE. Effect of smoking, alcohol and other factors on the selenium status of a healthy population. J Epidemiol Commun Health 1983;37:213-7. PubMed
  10. Capel ID, Jenner M, Williams DC, et al. The effect of prolonged oral contraceptive steroid use on erythrocyte glutathione peroxidase activity. J Steroid Biochem 1981;14:729-32. PubMed
  11. Contempre B, Dumont JE, Ngo B, et al. Effect of selenium supplementation in hypothyroid subjects of an iodine and selenium deficient area: the possible danger of indiscriminate supplementation of iodine-deficient subjects with selenium. J Clin Endocrinol PubMed
  12. Hofbauer LC, Spitzweg C, Magerstadt RA, Heufelder AE. Selenium-induced thyroid dysfunction. Postgrad Med J 1997;73:103-4. PubMed
  13. Debski B, Milner JA. Dietary selenium supplementation prolongs pentobarbital induced hypnosis. J Nutr Biochem 2004;15:548-53. PubMed
  14. Ishikawa M, Sasaki M, Koiwai K, et al. Inhibition of hepatic mixed-function oxidase enzymes in mice by acute and chronic treatment with selenium. J Pharmacobiodyn 1992;15:377-85. PubMed
  15. Lippmann SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the selenium and vitamin E cancer prevention trial (SELECT). JAMA 2009;301:39-51. DOI

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Selenium and Peginterferon alfa-2a Together: Common Questions

Is it safe to take Selenium with Peginterferon alfa-2a?
We do not list a known interaction between Selenium and Peginterferon alfa-2a. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Selenium and Peginterferon alfa-2a have any of the same side effects?
Yes — our sources link each of them separately to 9 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
Does Selenium interact with any other medications?
Yes. Selenium has 321 documented drug interactions in our database — Peginterferon alfa-2a is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Selenium monograph Uses, safety profile, and every drug interaction in one place Peginterferon Alfa-2a Injection drug information The full plain-English guide to this medication Peginterferon alfa-2a supplement interactions Every supplement checked against Peginterferon alfa-2a, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 36 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.