Drug & supplement interaction

Niacin + Desiccated Thyroid Extract

Desiccated Thyroid Extract brand names: Westhroid, WP Thyroid.

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

Niacin has a moderate interaction with Desiccated Thyroid Extract. 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 Desiccated Thyroid Extract

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

Moderate

THYROID HORMONE

Why this applies to Desiccated Thyroid Extract

Desiccated Thyroid Extract 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 the gist: desiccated thyroid extract (Westhroid, WP Thyroid) replaces the thyroid hormones your body isn't making enough of, mostly T4 and some T3. The concern with high-dose niacin is that it may lower a carrier protein in your blood called thyroxine-binding globulin and nudge your T4 levels down a bit. In plain terms, your thyroid medicine could end up working a little less than it should.

If that happened, you might notice hypothyroid-type symptoms creeping back, things like fatigue, feeling cold, weight gain, or sluggishness. Honestly, this is based mostly on lab-level and limited clinical findings, so it's not a sure thing, and ordinary food or vitamin amounts of niacin are unlikely to matter. It's really the prescription, drug-sized doses to watch. Please don't change anything on your own. Just check in with your pharmacist or doctor, who can run a simple thyroid blood test if needed.

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 Desiccated Thyroid Extract 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. Desiccated Thyroid Extract)
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 Desiccated Thyroid Extract

This page covers Niacin only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Desiccated Thyroid Extract page lists 38 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Tiratricol (major), Acetyl-l-carnitine (moderate), Alpha-lipoic Acid (moderate) and Ascophyllum Nodosum (moderate).

By severity: 2 major · 26 moderate · 10 minor.

From our pharmacist’s overview on the Desiccated Thyroid Extract page

“Activated charcoal is the first thing I would flag for anyone taking desiccated thyroid extract (Westhroid, WP Thyroid). It binds the medication in the gut and can sharply cut absorption, and it shares the major rating with tiratricol, itself a thyroid hormone that stacks on top of your prescribed dose.”

Reviewed by 2 · Jul 18, 2026

Open the Desiccated Thyroid Extract 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 Desiccated Thyroid Extract 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 Desiccated Thyroid Extract 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%

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

29 days ago today
Medication Desiccated Thyroid Extract
Top 25%

#660 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
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 Desiccated Thyroid Extract, 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 Desiccated Thyroid Extract supplement interactions › Every supplement checked against Desiccated Thyroid Extract, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Niacin and Desiccated Thyroid Extract Together: Common Questions

Can you take Niacin with Desiccated Thyroid Extract?
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 Desiccated Thyroid Extract 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 Desiccated Thyroid Extract 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.