Drug & supplement interaction

Niacin + Ospemifene

Ospemifene brand name: Osphena.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Niacin has a moderate interaction with Ospemifene. Theoretically, niacin might antagonize the therapeutic effects of thyroid hormones.

Read the full interaction report
SeverityModerate
LikelihoodProbable
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Niacin and Ospemifene

Here is the interaction we found between these two, with the evidence behind it.

Moderate

THYROID HORMONE

Why this applies to Ospemifene

Ospemifene falls under THYROID HORMONE — the group Niacin interacts with.

Theoretically, niacin might antagonize the therapeutic effects of thyroid hormones.
Clinical research and case reports suggests that taking niacin can reduce serum levels of thyroxine-binding globulin by up to 25% and moderately reduce levels of thyroxine (T4). Patients taking thyroid hormone for hypothyroidism might need dose adjustments when using niacin.
Severity Moderate Likelihood Probable Evidence D

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..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's something worth flagging: the interaction in our system is really about thyroid hormone medicines, not Ospemifene (Osphena). Ospemifene isn't a thyroid drug at all. It's an estrogen-like medicine you take by mouth to ease vaginal dryness and painful intercourse after menopause. So the specific concern on file, that high-dose niacin can lower thyroid hormone levels and weaken those drugs, doesn't really apply here.

I don't have solid evidence that niacin meaningfully changes how Ospemifene works. To be safe, I'd still mention any niacin supplement to your pharmacist or doctor, especially high prescription-strength doses, so they can double-check your full medication list. Everyday vitamin amounts of niacin are very unlikely to matter.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. O'Brien T, Silverberg JD, Nguyen TT. Nicotinic acid-induced toxicity associated with cytopenia and decreased levels of thyroxine-binding globulin. Mayo Clin Proc. 1992;67(5):465-8. PubMed
  2. Cashin-Hemphill L, Spencer CA, Nicoloff JT, et al. Alterations in serum thyroid hormonal indices with colestipol-niacin therapy. Ann Intern Med. 1987;107(3):324-9. PubMed
  3. Drinka PJ. Alterations in thyroid and hepatic function tests associated with preparations of sustained-release niacin. Mayo Clin Proc. 1992;67(12):1206. PubMed
  4. Shakir KM, Kroll S, Aprill BS, Drake AJ 3rd, Eisold JF. Nicotinic acid decreases serum thyroid hormone levels while maintaining a euthyroid state. Mayo Clin Proc. 1995;70(6):556-8. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction 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.
  • PossibleInteraction 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.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Niacin Also Interacts With Other Medications

Niacin has 726 moderate known drug interactions in our database — the Ospemifene one above is one of them. If you take anything else, check it against the full list below.

Moderate 726 No known interaction 2,104 (incl. Ospemifene)
Taking anything else?

Check Another of Your Medications Against Niacin

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

Everything else you take

See Every Supplement That Interacts With Ospemifene

This page covers Niacin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Ospemifene page lists 155 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Tiratricol (major) and Acacia Rigidula (moderate).

By severity: 4 major · 112 moderate · 39 minor.

From our pharmacist’s overview on the Ospemifene page

“Women prescribed ospemifene (Osphena) for painful intercourse after menopause are often the same women reaching for St. John's wort for mood or grapefruit juice at breakfast, and both sit among the four major-rated interactions on this page, so the list deserves genuine care.”

Reviewed by 2 · Jul 18, 2026

Open the Ospemifene interaction page

One more smart check

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

We hold 933 real supplement products containing Niacin, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Niacin. Your product may carry other ingredients that interact with Ospemifene too, on top of Niacin — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Niacin and Ospemifene 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 Niacin
Top 25%

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

29 days ago today
Medication Ospemifene
Steady interest

#2,440 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.

Supplement

About Niacin

What is Niacin?

Niacin
  • High cholesterol
  • Vitamin B3 deficiency (pellagra)
  • Heart health support
  • General energy and metabolism

Niacin (vitamin B3) is an essential nutrient your body needs for energy and metabolism, and deficiency is uncommon in most developed countries. Prescription-strength niacin has been used to adjust cholesterol levels, but high doses can cause flushing and other side effects and should only be taken under medical supervision. Always talk with a pharmacist or doctor before using high-dose niacin supplements.

Read the full Niacin monograph & all interactions
Medication

About Ospemifene

What Is Ospemifene Used For?

Brand name: Osphena

Osphena (ospemifene) is used to treat two specific symptoms of vulvar and vaginal atrophy — the thinning and drying of vaginal tissues that can happen after menopause. The first is moderate to severe dyspareunia (painful intercourse), and the second is moderate to severe vaginal dryness.

Both of these uses are for postmenopausal women only. Osphena is not used in children or in women who are pregnant or may become pregnant.

See full Ospemifene drug information
Keep checking

Other Drugs & Niacin

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

0Major
726Moderate
0Minor
2,103No known interaction
726 Moderate 2,103 No interaction
Moderate

726 interactions

Showing 60 of 726 moderate interactions — see all 726 on the Niacin page.

No interaction 2,103 drugs checked — show the list

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

Showing the 60 most looked-up of 2,103 medications checked with no known interaction — see the full Niacin list.

See the full Niacin interactions page
See every supplement checked against Ospemifene, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Niacin monograph › Uses, safety, and every drug interaction in one place Ospemifene supplement interactions › Every supplement checked against Ospemifene, ranked by severity Ospemifene drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Niacin and Ospemifene Together: Common Questions

Can you take Niacin with Ospemifene?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Niacin and Ospemifene interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Ospemifene and Niacin?

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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.