Drug & supplement interaction

Propionyl-l-carnitine + Thyroid Hormone

Thyroid Hormone brand name: Etwon.

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

Propionyl-l-carnitine has a moderate interaction with Thyroid Hormone. Theoretically, acetyl-L-carnitine might decrease the effectiveness of thyroid hormone replacement.

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

Propionyl-l-carnitine and Thyroid Hormone

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

Moderate

THYROID HORMONE

Theoretically, acetyl-L-carnitine might decrease the effectiveness of thyroid hormone replacement.
L-carnitine appears to act as a peripheral thyroid hormone antagonist by inhibiting entry of thyroid hormone into the nucleus of cells. Taking L-carnitine also seems to diminish some of the symptoms of hyperthyroidism. It is unclear if such an interaction would occur with propionyl-L-carnitine.
Severity Moderate Likelihood Possible Evidence B

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.

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

Here's the gist for your thyroid medicine (like levothyroxine or other thyroid hormone replacement): some forms of carnitine seem to act like a mild brake on thyroid hormone, keeping it from getting into cells and doing its job. In theory, that could make your thyroid medicine work a little less well, so symptoms of an underactive thyroid might creep back, things like tiredness, feeling cold, weight gain, or constipation.

I want to be honest about the evidence, though. This effect has mostly been seen with plain L-carnitine, not the propionyl form you're asking about, so we really don't know if propionyl-L-carnitine causes the same thing. It's more of a theoretical concern. Since thyroid dosing is sensitive, I'd run it by your pharmacist or doctor before adding it, and don't change your dose on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Benvenga S, Ruggeri RM, Russo A, et al. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Meta
  2. 12761 Benvenga S, Amato A, Calvani M, Trimarchi F. Effects of carnitine on thyroid hormone action. Ann N Y Acad Sci 2004;1033:158-67. 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

Propionyl-l-carnitine Also Interacts With Other Medications

Propionyl-l-carnitine has 18 moderate known drug interactions in our database — the Thyroid Hormone one above is one of them. If you take anything else, check it against the full list below.

Moderate 18 No known interaction 2,812 (incl. Thyroid Hormone)
Taking anything else?

Check Another of Your Medications Against Propionyl-l-carnitine

Covers the 2,830 medications we’ve checked against Propionyl-l-carnitine. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Thyroid Hormone

This page covers Propionyl-l-carnitine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Thyroid Hormone 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 Thyroid Hormone page

“The riskiest pairing on this page is tiratricol, which is itself a thyroid compound, so taking it alongside thyroid hormone (Etwon) stacks two doses of the same signal. It shares the list's only two major ratings with activated charcoal, which soaks up medication in the gut before the body can absorb it.”

Reviewed by 2 · Jul 18, 2026

Open the Thyroid Hormone interaction page

One more smart check

Taking Propionyl-l-carnitine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 57 real supplement products containing Propionyl-l-carnitine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Propionyl-l-carnitine. Your product may carry other ingredients that interact with Thyroid Hormone too, on top of Propionyl-l-carnitine — 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 Propionyl-l-carnitine and Thyroid Hormone 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 Propionyl-l-carnitine
Steady interest

#1,200 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Thyroid Hormone
Top 10%

#180 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 Propionyl-l-carnitine

What is Propionyl-l-carnitine?

  • Peripheral artery disease and leg pain
  • Heart and circulation support
  • Energy and exercise performance
  • Erectile dysfunction
  • Diabetic nerve pain

Propionyl-l-carnitine is a form of the amino acid derivative carnitine that the body uses to help turn fat into energy, and it is studied mostly for circulation problems like peripheral artery disease. Some evidence suggests it may help walking distance in people with poor leg circulation, but results are mixed and it is not a substitute for standard medical care. Talk to a pharmacist or doctor before using it, especially if you have a medical condition or take other medicines.

Read the full Propionyl-l-carnitine monograph & all interactions
Keep checking

Other Drugs & Propionyl-l-carnitine

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

0Major
18Moderate
0Minor
2,811No known interaction
18 Moderate 2,811 No interaction
Moderate

18 interactions

No interaction 2,811 drugs checked — show the list

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

Showing the 60 most looked-up of 2,811 medications checked with no known interaction — see the full Propionyl-l-carnitine list.

See the full Propionyl-l-carnitine interactions page
See every supplement checked against Thyroid Hormone, 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
Propionyl-l-carnitine monograph › Uses, safety, and every drug interaction in one place Thyroid Hormone supplement interactions › Every supplement checked against Thyroid Hormone, 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 Propionyl-l-carnitine and Thyroid Hormone Together: Common Questions

Can you take Propionyl-l-carnitine with Thyroid Hormone?
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 Propionyl-l-carnitine and Thyroid Hormone 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 Thyroid Hormone and Propionyl-l-carnitine?

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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.