Medicine caution
L-carnitine thyroid cautions: one trial, side effects and warfarin
L-carnitine thyroid cautions rest on one 2001 trial: in 50 women taking levothyroxine, 2 or 4 g a day for 6 months worked against thyroid hormone. We found no source on L-carnitine and warfarin. Flow Nerves names L-carnitine and prints no amount, so ask a pharmacist if you take thyroid medicine.
Written by the Flow Nerves label deskUpdated · 5 min read
The trial
What is the L-carnitine thyroid medicine concern?
L-carnitine thyroid medicine is a concern because a 2001 trial in 50 women on levothyroxine found L-carnitine worked against thyroid hormone.
The women took 2 or 4 g a day for 6 months (Benvenga 2001, L-carnitine and thyroid hormone). That is a gram-scale dose, and the trial's abstract also states that carnitine has no drug interactions, so treat this as a reported effect at gram doses, not a settled rule. Flow Nerves prints no amount, and no trial tested it.
| Medicine or condition | What we found |
|---|---|
| Thyroid hormone | 2 or 4 g a day worked against it in 50 women (Benvenga 2001, L-carnitine and thyroid hormone) |
| Seizure disorders, valproic acid and other anticonvulsants | NIH warns of seizures and lists an interaction (NIH ODS, Carnitine) |
| Warfarin | We found no source |
Warfarin
Does L-carnitine affect warfarin?
We found no source that says so, and none that says it does not.
The NIH carnitine sheet does not discuss warfarin. So we state no warfarin finding and no blood-test advice. If you take warfarin, a pharmacist is the right person to ask, and your prescriber decides about any testing. Do not stop or change a prescribed medicine because of a supplement.
Side effects and signs
What are the L-carnitine side effects?
NIH says about 3 g a day can cause nausea, vomiting, abdominal cramps, diarrhea and a fishy body odor (NIH ODS, Carnitine).
- Sudden numbness or weakness on one side, trouble speaking, seeing or walkingCall 911. CDC lists these as stroke signs.
- Dark urine, yellow skin or eyes, belly pain, fatigueCan be signs of liver trouble, which LiverTox links to turmeric. Stop and get medical care the same day.
- Unusual bruising, nosebleeds or blood in urine or stoolPossible bleeding, especially on a blood thinner (MSK on turmeric and CoQ10). Stop and call your clinician or pharmacist.
- Shaky, sweaty, confused, very hungryPossible low blood sugar if you take diabetes medicine (MSK on alpha lipoic acid): treat it as your care team told you and call them.
- Rash, hives or swellingPossible allergy. Stop and get medical help; swelling of the face or throat or trouble breathing is an emergency.
- Diarrhea, nausea, stomach crampsCommon supplement effects (NIH on magnesium and carnitine). Stop and ask a clinician if they persist.
Signs from (CDC, Stroke signs and symptoms) (LiverTox, Turmeric) (MSK, Alpha-lipoic acid) (NIH ODS, Magnesium). This list is not complete. A supplement is never a reason to wait.
Flow Nerves capsule: 30 a bottle1 capsule a day per the seller's FAQ · 2, 3 or 6 bottles · 2 bottles at $79 each · other prices at checkout
See the priceWhat to ask
What should you ask a pharmacist about carnitine?
Bring the bottle and your full medicine list, thyroid hormone and blood thinners included.
Tell every provider about every supplement and keep a record (NIH ODS, Dietary Supplements: What You Need to Know). Keep taking prescribed medicine. Sudden numbness or weakness, especially on one side, trouble speaking, chest pain or trouble breathing: call 911. Lasting tingling needs a clinician to look for a cause.
Where Flow Nerves fits
Does this apply to Flow Nerves?
Possibly, if you take thyroid hormone, because L-carnitine is one of its six named ingredients.
We hold no Supplement Facts panel. See the medicine interactions guide.
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See 6 bottlesDollar amounts for these two packs are shown at the live checkout; the seller's brief printed none (Flow Nerves sales site). Two bottles are also sold at $79 each. If you take blood thinners, diabetes medicine or thyroid hormone, ask a clinician or pharmacist before you order.
FAQ
Flow Nerves questions people ask
Does L-carnitine interfere with levothyroxine?
A 2001 trial in 50 women on levothyroxine found 2 or 4 g a day for 6 months worked against thyroid hormone. Ask a pharmacist before combining them, and never change a prescribed medicine on your own.
Does L-carnitine cause a fishy smell?
NIH lists a fishy body odor among effects at about 3 g a day, along with nausea, vomiting, abdominal cramps and diarrhea. Flow Nerves prints no amount, so we cannot say how close a capsule is to that dose.
Is L-carnitine a problem for seizure disorders?
NIH warns of seizures in people with seizure disorders and lists valproic acid and other anticonvulsants as interactions. Ask your clinician or pharmacist first.
Who wrote this
Written and reviewed by
Pages built from the bottle render, the seller's brief 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 of a licensed U.S. retail desk for Flow Nerves. It is not the manufacturer, and we have not been given the name of the maker. We earn money when you buy through our order links.
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Check your medicines first, and ask a clinician or pharmacist if you take blood thinners, diabetes medicine or thyroid hormone. Then pick a pack: 2, 3 or 6 bottles of 30 capsules. The 2-bottle pack is listed at $79 a bottle; the other prices are shown at checkout. A 60-day satisfaction promise is listed, so confirm the live policy.
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