If you are currently being treated with any of the following medications, you should not use carnitine without first talking to your healthcare provider.

AZT
In a laboratory study, L-carnitine supplements protected muscle tissue against toxic side effects from treatment with AZT, a medication used to treat human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS). Additional studies are needed to confirm whether L-carnitine would also have this effect in people.

Doxorubicin
Treatment with L-carnitine may protect heart cells against the toxic side effects of doxorubicin, a medication used to treat cancer, without reducing the effectiveness of this chemotherapy agent.

Isotretinoin
Isotretinoin, a strong medication used for severe acne, can cause abnormalities in liver function, measured by a blood test, as well as elevations in cholesterol and muscle pain and weakness. These symptoms are similar to those seen with carnitine deficiency. Researchers in Greece showed that a large group of people who had side effects from isotretinoin got better when taking L-carnitine compared to those who took a placebo.

Valproic Acid
The anticonvulsant medication valproic acid may lower blood levels of carnitine and can cause carnitine deficiency. Taking L-carnitine supplements may prevent deficiency and may also reduce the side effects of valproic acid.