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This list does not cover all possible side effects. Contact your doctor or pharmacist if you notice any other side effects.
Acetyl-L-carnitine was safe and well-tolerated in most clinical trials. In rare cases, it caused:
- • Upset stomach
- • Vomiting
- • Diarrhea
- • Headache
- • Insomnia
Our bodies partly metabolize carnitine into trimethylamine-N-oxide (TMAO), which may promote plaque build-up in blood vessels (atherosclerosis). In a study of over 2,500 people, those with higher blood levels of L-carnitine had increased rates of heart disease.
There are various ways to lower your TMAO levels, such as eating more vegetables, dietary fiber, probiotic – and resveratrol-rich foods.
L-carnitine supplementation may cause unpleasant fishy odor and suppress thyroid hormones. ALCAR might do the same, but studies haven’t confirmed this.
Acetyl-L-carnitine is likely safe for long-term use. It might contribute to heart disease and suppress thyroid hormones, but more research is needed to confirm this.
Sensitive Groups
Safety data about acetyl-L-carnitine during pregnancy is lacking, while the evidence for L-carnitine is limited. If you’re pregnant or trying to conceive, stay on the safe side and avoid ALCAR supplements.
Acetyl-L-carnitine appears to be safe for children, but they should use it under strict medical supervision. *
When taken by mouth: Acetyl-L-carnitine is LIKELY SAFE for most people. It can cause some side effects including stomach upset, nausea, vomiting, dry mouth, headache, and restlessness. It can also cause a "fishy" odor of the urine, breath, and sweat.
When given by IV: Acetyl-L-carnitine is POSSIBLY SAFE for most adults when given intravenously (by IV). Use only under medical supervision.
Special Precautions & Warnings:
Pregnancy and breast-feeding: There isn't enough reliable information to know if acetyl-L-carnitine is safe to use when pregnant or breast-feeding. Stay on the safe side and avoid use.
Children: Acetyl-L-carnitine is
POSSIBLY SAFE for most children when taken by mouth.
Bipolar disorder: Acetyl-L-carnitine might worsen symptoms in people with bipolar disorder who are currently in remission.
Nerve damage in the hands and feet caused by cancer drug treatment: Acetyl-L-carnitine might worsen symptoms in some people with nerve pain caused by a class of chemotherapy drugs known as taxanes.
Underactive thyroid (hypothyroidism): There is some concern that acetyl-L-carnitine might interfere with thyroid hormone. Don't use acetyl-L-carnitine if you have an under-active thyroid.
Seizures: An increase in the number or seriousness of seizures has been reported in people with a history of seizures who have used L-carnitine by mouth or by IV (intravenously). Since L-carnitine is related to acetyl-L-carnitine, there is a concern that this might also occur with acetyl-L-carnitine. If you have ever had a seizure, don't take acetyl-L-carnitine.
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