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What Are the Side Effects of L-Carnitine?
L-carnitine side effects show up mostly at high doses: about 3 g a day can cause nausea, vomiting, cramps, diarrhea and a fishy body odor. Synaptril lists L-carnitine fourth in its blend with no printed amount, and our math caps it at about 58 mg a capsule.
Written by the Synaptril label deskUpdated · 4 min read
What are the side effects of L-carnitine?
The side effects of L-carnitine are stomach trouble and a fishy smell. At about 3 g a day, the NIH reports nausea, vomiting, abdominal cramps, diarrhea and a "fishy" body odor (NIH ODS, Carnitine).
| Level | What is reported |
|---|---|
| Trials | About 1 to 4 g a day |
| Around 3 g a day | Nausea, cramps, diarrhea, fishy odor |
| Synaptril capsule | At most about 58 mg by our math |
What is the TMAO concern?
TMAO is a compound that gut bacteria make from carnitine that is not absorbed. It has been linked to cardiovascular disease risk, though NIH says the meaning is not well understood (NIH ODS, Carnitine).
So this is an open question, not a warning label. A small capsule dose is a small input to it.
Which medicines interact with L-carnitine?
Some seizure drugs lower carnitine levels. The NIH names valproic acid, phenobarbital, phenytoin and carbamazepine, along with pivalate-conjugated antibiotics (NIH ODS, Carnitine).
If you take any of these, ask your prescriber before adding a carnitine product. Keep taking prescribed medicine.
Tap a number to read that part of the panel.
- Serving
Serving size 1 capsule; 30 servings per container.
- Magnesium 80 mg
As magnesium glycinate from the proprietary blend: 19% of the Daily Value.
- 19% DV
The Daily Value for magnesium is 420 mg, so 80 mg is 19%.
- Proprietary blend, 575 mg
Six ingredients share 575 mg, listed most to least by weight.
- The six lines
Magnesium glycinate, alpha lipoic acid, butcher's broom root, L-carnitine, turmeric (95% curcuminoids), CoQ10.
- Other ingredients
The capsule shell and flow agents. No sweetener, caffeine or color is listed.
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See packsHow does one capsule compare with the doses that caused trouble?
A Synaptril capsule is far below the doses linked to side effects. The ceiling of about 58 mg is roughly 17 times smaller than the 1 g low end of trial doses, and about 52 times smaller than 3 g.
The arithmetic is plain: 1,000 divided by 58 is about 17, and 3,000 divided by 58 is about 52. The label prints no amount, so these are ceilings, not measurements.
- Gram-level doses are where stomach effects and fishy odor were reported (NIH ODS, Carnitine).
- Other lines in the blend can also loosen stools, so a symptom may not come from carnitine.
- Call a clinician if a symptom persists.
Where can you read more?
Read the L-carnitine profile and the Synaptril side effects page. Related: L-carnitine vs acetyl-L-carnitine.
FAQ01
Synaptril questions people ask
Does L-carnitine make you smell fishy?
At about 3 g a day it can, according to the NIH. A Synaptril capsule holds far less, at most about 58 mg by our math, so the odor is unlikely, though the label cannot confirm the amount.
Can L-carnitine cause diarrhea?
Yes, at higher doses. Around 3 g a day has caused nausea, cramps and diarrhea. Magnesium can also loosen stools at high doses, so a mix is possible. Call a clinician if it persists.
Is the TMAO risk from L-carnitine proven?
No. NIH links TMAO to cardiovascular risk but says the implications are not well understood. We do not call it a proven harm.
Does L-carnitine interact with seizure medicine?
Yes, in one direction. The NIH says valproic acid, phenobarbital, phenytoin and carbamazepine can lower carnitine levels (NIH ODS, Carnitine). Tell your prescriber before adding a carnitine product, and do not change a dose yourself.
Who wrote this02
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Pages built from the label, the sales page and linked NIH, FDA, CDC, FTC and peer-reviewed sources.
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