L-carnitine is an amino acid, one of the building blocks for proteins. It is naturally produced in the body. It can help increase the rate at which a body burns fat, increase energy levels and promote a healthy heart, circulation and liver. As a supplement, it's used most frequently by dieters for weight loss, by bodybuilders for muscle mass, and by athletes for sports endurance. Although generally safe, l-carnitine can produce side effects in some cases.
Allergic Reactions
As with all supplements, a few individuals may experience an allergic reaction to l-carnitine. Symptoms of this condition can include hives, rashes and itching; swelling of the mouth, lips, throat or hands; a tingling in the mouth and throat; chest tightness and wheezing or trouble breathing.
Mental/Neurological Reactions
Patients with Alzheimer's disease who have taken l-carnitine have exhibited increased agitation, confusion, depression, aggression and manic behavior, says Dr. Andrew Weil. However, it's not completely clear whether the effects are due to the l-carnitine or to the disease. L-carnitine supplements have also been shown to increase the number and intensity of seizures in patients with a history of seizures, according to a study published in a 2001 issue of the "Physicians Desk Reference for Nutritional Supplements."
Insomnia
Stronger doses of l-carnitine can cause energy spikes leading to difficulties falling asleep. It's recommended that you take l-carnitine supplements earlier in the day to avoid this problem.
Digestive Disorders
Doses of 5g of l-carnitine or more per day can cause dyspepsia, heartburn and diarrhea, as reported in a 2001 edition of "Cardiovascular Research." That same study found that supplements of 3,000mg per day or more can cause a "fishy" body odor.
Thyroid
Although l-carnitine supplementation has been found to benefit hyperthyroid patients, it can block the thyroid if taken in high doses. Most experts recommend against l-carnitine if you have low or borderline thyroid levels, since l-carnitine can impair the action of your thyroid hormone medications.
Cardiovascular
In rare cases, especially with high doses, l-carnitine can cause fast heartbeat rates, hypertension--or an increase in your blood pressure--and fever, according to a study in a 2001 "American Journal of Kidney Disease."
Kidneys
Patients with kidney disease should avoid taking l-carnitine. The Food and Drug Administration found that myasthenia, or a progressive weakness of muscle groups, was seen in kidney patients on dialysis who also took l-carnitine supplements.
Anorexia
L-carnitine is often used for weight loss because it helps to decrease the appetite. If taken to extremes, it can cause a form of anorexia nervosa, an eating disorder that can lead to starvation.
Drug Interactions
Avoid taking l-carnitine if you are also taking acenocoumarol (Sintrom), which is used to slow blood clotting, as l-carnitine can slow blood clotting too much. Likewise, if l-carnitine is used with another drug used to slow clotting, warfarin (Coumadin), it can increase the effects of the drug and lead to bruising and bleeding.
Miscellaneous Side Effects
In their study published in "Neuropsychobiology," researchers Dr. Audrius Plioplys and Dr. Sigita Plioplys found that less frequent side effects of l-carnitine supplements can occur, including flu syndrome, a reaction at the site of an injectable form of the drug, pain, pharyngitis and headache.
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