Drug & supplement interaction

Propionyl-l-carnitine + Liothyronine

Liothyronine brand name: Cytomel.

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

Propionyl-l-carnitine has a moderate interaction with Liothyronine. 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 Liothyronine

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

Moderate

THYROID HORMONE

Why this applies to Liothyronine

Liothyronine falls under THYROID HORMONE — the group Propionyl-l-carnitine interacts with.

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 if you take liothyronine (Cytomel) for an underactive thyroid and you're eyeing propionyl-L-carnitine for leg circulation. Carnitine seems to work as a mild thyroid hormone blocker, getting in the way of thyroid hormone entering your cells where it does its job. So in theory, the supplement could chip away at how well your liothyronine works, leaving you with lingering low-thyroid symptoms like fatigue, feeling cold, weight creep, or low mood.

Now, the honest part: this effect was mostly seen with regular L-carnitine, and it isn't clear the propionyl form acts the same way. The evidence here is on the weaker side, so I wouldn't panic. Liothyronine is potent and dosed carefully, though, so before adding this supplement, check with your pharmacist or doctor and keep an eye on your thyroid labs.

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 Liothyronine 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. Liothyronine)
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.

From our Q&A

Questions About Propionyl-l-carnitine or Liothyronine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Propionyl-l-carnitine or Liothyronine, 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.

Everything else you take

See Every Supplement That Interacts With Liothyronine

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

“Liothyronine (Cytomel) is the active thyroid hormone T3, and it does not tolerate interference well. Of the 38 supplements and herbs on file, 21 act on thyroid function itself, some amplifying the hormone and others blunting it, iodine-rich seaweeds able to swing either way.”

Reviewed by 2 · Jul 18, 2026

Open the Liothyronine 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 Liothyronine 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 Liothyronine 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
Top half

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

29 days ago today
Medication Liothyronine
Top 25%

#336 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
Medication

About Liothyronine

What Is Liothyronine Used For?

Brand name: Cytomel

Liothyronine (available as tablets under the brand names Cytomel, Liomny, and Liothyronine Sodium, and as an injection under Liothyronine Sodium and Triostat) is primarily used to treat hypothyroidism (an underactive thyroid) across all its forms — whether the cause is in the thyroid itself, the pituitary gland, or the hypothalamus, and whether it was present at birth or developed over time.

The oral tablets are also used alongside surgery and radioiodine therapy to suppress TSH (thyroid-stimulating hormone) in people with well-differentiated thyroid cancer, and as a diagnostic agent in thyroid suppression tests. Liothyronine sodium injection is specifically indicated for myxedema coma (a life-threatening form of severe hypothyroidism) and may be used in patients who are allergic to thyroid products derived from pork or beef.

See full Liothyronine drug information
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 Liothyronine, 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 Liothyronine supplement interactions › Every supplement checked against Liothyronine, ranked by severity Liothyronine 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 Propionyl-l-carnitine and Liothyronine Together: Common Questions

Can you take Propionyl-l-carnitine with Liothyronine?
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 Liothyronine 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 Liothyronine 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.