Medicine safety
L-Carnitine and Thyroid Medicine: What One Trial Shows
L-carnitine and thyroid medicine were studied together in one 2001 trial of 50 women taking levothyroxine. At 2 to 4 grams a day, carnitine acted against the thyroid hormone. Flow Nerves lists L-carnitine and prints no amount, so ask a pharmacist if you take thyroid medicine.
Written by the Flow Nerves label deskUpdated · 4 min read
The trial
Does L-carnitine affect thyroid medicine?
In one trial it did. Benvenga and colleagues, in 2001, gave 50 women a thyroid-suppressing dose of levothyroxine and added 2 or 4 grams a day of oral L-carnitine (Benvenga 2001, Carnitine and thyroid hormone).
The trial ran 6 months, with carnitine for 2 or 4 of those months. Carnitine reversed or minimized symptoms of too much thyroid hormone, which the authors read as carnitine acting against thyroid hormone in some tissues (Benvenga 2001, Carnitine and thyroid hormone).
This is one small trial in one group of women. It shows an interaction is known, not how common it is.
Doses on one scale
How big were the L-carnitine doses?
The doses were large: 2,000 to 4,000 mg a day. For comparison, the NIH says about 3,000 mg a day of carnitine supplements can cause nausea, vomiting, cramps, diarrhea and a fishy body odor (NIH ODS, Carnitine).
The bars show those study amounts, with the dashed bar for the Flow Nerves amount. It is dashed because the label prints no figure.
These are amounts a study used. They are not what a Flow Nerves capsule holds.
What it cannot tell us
Can this trial tell you if Flow Nerves is a problem?
No. The label prints no L-carnitine amount, and the form is not stated. L-carnitine and acetyl-L-carnitine are different compounds, and MSK says they are not the same (MSK, Carnitine).
| Question | Answer |
|---|---|
| Was Flow Nerves tested? | No study of it exists in our sources |
| Is a capsule near 2,000 mg? | Unknown; no amount is printed |
| Which carnitine form? | Not stated on the material we have |
| Who was studied? | 50 women on levothyroxine |
What to do
Should you ask a pharmacist about carnitine and thyroid medicine?
Yes, if you take levothyroxine or any thyroid medicine. Say that the label lists L-carnitine with no amount, and ask whether your thyroid tests need a closer look.
Keep taking prescribed medicine. NIH also lists some antibiotics and seizure medicines as interacting with carnitine (NIH ODS, Carnitine).
FAQ
Flow Nerves questions people ask
Can L-carnitine interfere with levothyroxine?
One 2001 trial found L-carnitine at 2 to 4 g a day acted against thyroid hormone in women on levothyroxine (Benvenga 2001, Carnitine and thyroid hormone). Ask your pharmacist if you take it.
How much L-carnitine is in Flow Nerves?
The label does not say. No milligram amount is printed in the material we have, and the carnitine form is not stated.
Does L-carnitine affect an underactive thyroid?
We found no source on that. The trial we read tested women taking a suppressive dose of levothyroxine. Ask your doctor about your own condition.
Should I stop my thyroid pill?
No. Keep taking prescribed medicine exactly as directed, and ask your doctor or pharmacist before adding a supplement.
Who wrote this
Written and reviewed by
Pages built from the label, the brand panels and linked NIH, FDA, CDC, FTC and peer-reviewed sources.
Last updated . Read our editorial standards and how we check reviews. This website is the information site for a U.S. stocking partner for Flow Nerves. It is not the manufacturer or a distributor named on the label. We earn money when you buy through our order links.
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