Avoid in individuals with a known allergy or hypersensitivity to carnitine.
Side Effects and Warnings
In general, L-carnitine is safe and no significant complications have been reported in available human clinical studies. Minor adverse effects have been reported with the use of L-carnitine or acetyl-L-carnitine, such as skin rash, body odor, "fishy smell," diarrhea, gastric pyrosis (heartburn), nausea, gastralgia (stomachache), loose bowel movement, nonspecific abdominal discomfort, or vomiting. Euphoria, insomnia, nervousness, mania, depression, and aggression have also been reported, but primarily in patients with pre-existing psychiatric conditions.
Transient hair loss was reported in 1% of cases. Less birth weight was regained in low birth weight infants treated with L-carnitine.
Carnitine supplements should be used cautiously in patients with peripheral vascular disease, hypertension (high blood pressure), alcohol-induced liver cirrhosis, low birth weight (infants), diabetics, and patients on hemodialysis.
Pregnancy and Breastfeeding
L-carnitine is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence.
Adults (18 years and older):
The U.S. Food and Drug Administration (FDA) recommends 1 gram of L-carnitine three times per day, intravenously (injected), for primary and secondary carnitine deficiency; this dose should not exceed 3 grams per day. A variety of doses have been used, with 3 grams per day in divided doses for 2-4 months being the most common; however, the doses range from 1 to 9 grams per day. Conditions treated have included AIDS, memory in alcoholics, Alzheimer's disease, angina (chest pain), congestive heart failure, depression, diabetes, diabetic neuropathy, dialysis, exercise performance, hepatic encephalopathy (brain disease), hyperlipidemia (high cholesterol), hyperthyroidism, myocardial infarction (heart attack), peripheral neuropathy (nerve damage), and peripheral vascular disease.
Intravenous (needle into a vein) injections have also been used, with doses typically ranging from 15-50 milligrams per kilogram twice daily. Injections have been given for seven days up to one year. Higher doses (up to 9 grams per day) have been studied. Injections should only be given under the supervision of a qualified healthcare professional.
The U.S. Food and Drug Administration (FDA) does not recommend exceeding 3 grams carnitine daily for primary and secondary carnitine deficiency. A typical dose for these deficiencies, as well as Rett's syndrome, is 100-200 milligrams per kilogram taken daily divided over two or three doses. For hyperlipidemia (high cholesterol), 3 grams L-carnitine for up to six weeks has been used. For total parental nutrition in infants, 50 micromoles per kilogram for two weeks has been used. Injections should only be given under the supervision of a qualified healthcare professional.
Interactions with Drugs
Several drugs may affect the levels of carnitine in the body. For example, adefovir dipivoxil (Hepsera®), which is given for hepatitis B, may reduce free carnitine levels. Cephalosporin antibiotics may reduce plasma carnitine levels. Anticonvulsants (phenobarbital, phenytoin, carbamazepine) may decrease serum carnitine in children. Cisplastin may increase urinary excretion of carnitine. Ifosfamide (Mitoxana®), a chemotherapy drug, may increase urinary loss of carnitine; however, use of carnitine plus ifosfamide may help reduce fatigue (side effect of ifosfamide treatment). Patients suffering from neuropathy (nerve damage) induced by nucleosides may have reduced levels of acetyl carnitine. Penicillin derivatives (pivaloyloxymethyl esterified, pivampicillin, and pivmecillinam) may decrease the serum carnitine concentration, elevate excretion of acyl-carnitine, and reduce muscle carnitine concentration in adults and children.
L-carnitine may decrease the need for certain drugs, such as glycosides, digoxin, diuretics, beta-blockers, channel blockers, hypolipidemic (cholesterol-altering) drugs, and nitro derivatives.
L-carnitine supplementation may reduce side effects associated with interleukin-2 (IL-2) or nortriptyline (Pamelor®, Aventyl®). It may also improve liver and muscular side effects associated with isotretinoin (Accutane®) in acne patients. Carnitine may reduce nerve damage symptoms associated with paclitaxel (Taxol®) use.
Carnitine may prevent arrhythmias (abnormal heart rhythms) provoked by adriamycin (Doxorubicin®), which is used in chemotherapy. L-carnitine may decrease the need for antiarrhythmics (medications used to treat abnormal rhythms in the heart). Carnitine plus propafenone may improve arrhythmia (heart rhythm) better than propafenone alone.
L-carnitine may decrease the need for anticoagulants ("blood thinners"), such as warfarin (Coumadin®) or heparin.
Several combinations have shown positive interactions. For example, sildenafil and propionyl-L-carnitine may be more effective than sildenafil alone. Although not well studied in humans, L-carnitine used concurrently with antiviral agents such as zidovudin (Retrovir®) or carnitine used with nortryptiline may also have a positive interaction that reduces side effects. L-carnitine plus acetyl-L-carnitine plus cinnoxicam has been found more effective in improving sperm parameters as compared with L-carnitine plus acetyl-L-carnitine alone.
Patients with diabetes should use caution because L-carnitine may decrease blood sugar. However, carnitine levels did not change in diabetics using insulin or sulfonylurea therapy. It is unclear whether L-carnitine would have similar effects when combined with other medications that lower blood sugar. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.
Although not well studied in humans, carnitine may increase valproic acid concentrations in the brain, which might increase the effects of valproic acid. Caution is advised.
Interactions with Herbs and Dietary Supplements
L-carnitine may decrease the need for herbs or supplements with anticoagulant effects ("blood thinners"). L-carnitine may also decrease the need for herbs or supplements with diuretic effects. Dosing adjustments may be necessary.
Patients with diabetes should use caution because L-carnitine may decrease blood sugar. However, carnitine levels did not change in diabetics using insulin or sulfonylurea therapy. It is unclear whether L-carnitine would have similar effects when combined with other herbs and supplements that lower blood sugar. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.
Choline supplementation may reduce excretion, renal (kidney) clearance, and fractional clearance of non-esterified carnitine.
L-carnitine chloride and potassium chloride may minimize rhabdomyolysis, a side effect of taking licorice by mouth.