Blog
L-Carnitine Side Effects, TMAO and Body Odor
L-carnitine side effects are nausea, vomiting, stomach cramps, diarrhea and a fishy body odor, mostly near 3 g a day. Gut bacteria turn unabsorbed carnitine into TMAO, which may raise heart disease risk, though the meaning is not well understood. Synaptril lists L-carnitine fourth in its blend, at no more than 144 mg.
Written by the Synaptril label deskUpdated · 4 min read
The short answer01
What are the side effects of L-carnitine?
L-carnitine side effects at about 3 g a day are nausea, vomiting, abdominal cramps, diarrhea and a fishy body odor (NIH ODS, Carnitine).
The NIH says carnitine has no RDA and no set upper limit. Supplements range from about 3 mg to 5,000 mg (NIH ODS, Carnitine). That wide spread is why the amount on the bottle matters.
The NIH sheet also notes that some antibiotics and seizure drugs lower carnitine levels in the body. It does not discuss warfarin or thyroid hormone, so those questions are open (NIH ODS, Carnitine).
The TMAO debate02
What is TMAO and should you worry about it?
TMAO is a compound made when gut bacteria break down carnitine that was not absorbed. It may raise the risk of heart disease, but the NIH says the implications are not well understood (NIH ODS, Carnitine).
So the honest answer is mixed. The link is being studied, no one has set a safe or unsafe dose from it, and our sources give no number to apply to a single capsule.
| Effect | When it appears | Status |
|---|---|---|
| Nausea, cramps, diarrhea | About 3 g a day | Documented (NIH ODS, Carnitine) |
| Fishy body odor | About 3 g a day | Documented (NIH ODS, Carnitine) |
| TMAO rise | Unabsorbed carnitine meets gut bacteria | Meaning unclear (NIH ODS, Carnitine) |
| Memory benefit | Acetyl form, 1.5 to 3 g a day | Unclear; Cochrane found no clinically important gain (Cochrane, Acetyl-L-carnitine dementia) |
In Synaptril03
How much L-carnitine is in Synaptril?
The label does not say. L-carnitine is fourth in the 575 mg blend, so it holds at most 144 mg per capsule.
Take a worked case. Pure magnesium glycinate takes about 570 mg, which leaves roughly 8 mg for the other five. In a generous case, where the glycinate weighs 400 mg, L-carnitine gets at most 58 mg. That 20% figure is our assumption, not a published number.
Even the 144 mg ceiling is under 5% of the 3 g that causes gut trouble. The generous case of 58 mg is about 2%. So the side effects above are unlikely at one capsule a day.
The flip side: the memory trials used acetyl-L-carnitine at 1.5 to 3 g (NIH ODS, Carnitine), a different form at far higher doses. Those results do not carry over. See the L-carnitine page.
Carnitine also comes from food and other supplements. If you take another carnitine product, add the amounts.
Synaptril: from $49 a bottle30 capsules · 2, 3 or 6 bottles · free shipping on 3 or 6 · 60-day guarantee
See packsCare04
Who should ask a doctor before taking L-carnitine?
Ask first if you have heart disease, take seizure medicine or a blood thinner, or are pregnant or nursing.
The label says to consult a physician if you take a medication or have a medical condition. It is also not for those under 18. Keep taking any prescribed medicine, and do not change it because of a supplement.
The side effects page lists cautions for all six ingredients.
FAQ05
L-carnitine side effect questions
Does L-carnitine make you smell like fish?
It can at about 3 g a day (NIH ODS, Carnitine). Gut bacteria produce a compound that gives the odor. At Synaptril's likely amount, far under that, the odor is unlikely. If you notice it, stop and ask a pharmacist.
Is the TMAO link to heart disease proven?
No. The NIH says TMAO may raise cardiovascular risk but the implications are not well understood (NIH ODS, Carnitine). People with heart disease should ask their doctor before using any carnitine product.
What dose of L-carnitine is considered too high?
No upper limit is set. Side effects such as nausea and cramps appear near 3 g a day (NIH ODS, Carnitine). Synaptril's label caps the L-carnitine amount at 144 mg by blend math, well under that.
Is acetyl-L-carnitine the same as L-carnitine?
No. They are related forms. Memory trials used acetyl-L-carnitine at 1.5 to 3 g a day (NIH ODS, Carnitine), and a Cochrane review of 16 trials found no clinically important benefit (Cochrane, Acetyl-L-carnitine dementia). Synaptril lists plain L-carnitine.
Can L-carnitine interact with my medicines?
Possibly. Some antibiotics and seizure drugs lower carnitine levels (NIH ODS, Carnitine). The NIH sheet does not cover warfarin or thyroid hormone, so check with your pharmacist if you take either.
Does L-carnitine come from food too?
Yes. The body makes it and foods supply it. Supplement amounts are what raise concerns. Our sources do not give a food total for Synaptril users, so count other carnitine products you take and mention them to your doctor.
Who wrote this06
Written and reviewed by
Pages built from the label, the sales page and linked NIH, FDA, CDC, FTC and peer-reviewed sources.
Last updated . See our editorial standards and how we check reviews. This website is run by Getsynaptril, a stocked U.S. Synaptril counter, not by the manufacturer or the distributor. We are paid when you buy through our order links.
Keep reading
More Synaptril pages
Stocked U.S. Synaptril counter
Ready to try Synaptril?
Check your medicines first, then pick a pack. Three or six bottles ship free and cost less per bottle, and every pack carries the 60-day money-back guarantee.
- Secure BuyGoods checkout
- 60-day money-back guarantee
- Ships from the U.S.
