From the Guidelines
L-carnitine supplementation should be approached with caution due to potential side effects, including nausea, vomiting, stomach cramps, diarrhea, and a fishy body odor, particularly at doses of approximately 3 g/day 1.
Benefits of L-Carnitine
The benefits of L-carnitine supplementation include improved exercise performance, enhanced recovery after workouts, and increased fat burning. It may also support heart health by improving cardiac function and reducing inflammation. For those with certain medical conditions, L-carnitine supplementation at doses of 500-2000 mg daily can help manage symptoms of peripheral artery disease, improve cognitive function in the elderly, and assist in managing certain metabolic disorders.
Side Effects of L-Carnitine
However, L-carnitine supplementation can cause side effects, including:
- Nausea
- Vomiting
- Stomach cramps
- Diarrhea
- A fishy body odor Higher doses may increase the risk of gastrointestinal issues. People with seizure disorders, kidney disease, or those taking certain medications should consult healthcare providers before supplementation.
Mechanism of Action
L-carnitine works by facilitating the transport of long-chain fatty acids into mitochondria where they can be broken down to produce energy, making it particularly beneficial for activities requiring endurance and for individuals with conditions affecting energy metabolism. According to the espen micronutrient guideline, at doses of approximately 3 g/day, carnitine supplements can cause nausea, vomiting, abdominal cramps, diarrhea, and a “fishy” body odor 1.
Clinical Evidence
A study published in the journal Circulation found that propionyl-L-carnitine, a congener of L-carnitine, improved maximal walking distance by 54% to 73% in patients with intermittent claudication 1. However, it is essential to weigh the potential benefits against the potential side effects and consult with a healthcare provider before supplementation.
From the FDA Drug Label
ADVERSE REACTIONS The following adverse reactions associated with the use of oral formulations of levocarnitine were identified in clinical trials or postmarketing reports. Because these reactions were reported voluntarily from a population of uncertain size, it is not always possible to estimate their frequency, reliability, or to establish a causal relationship to drug exposure Gastrointestinal Reactions: Various mild gastrointestinal complaints have been reported during the long-term administration of oral L- or D,L-carnitine; these include transient nausea and vomiting, abdominal cramps, and diarrhea. INDICATIONS AND USAGE CARNITOR® (levocarnitine) is indicated in the treatment of primary systemic carnitine deficiency. In the reported cases, the clinical presentation consisted of recurrent episodes of Reye-like encephalopathy, hypoketotic hypoglycemia, and/or cardiomyopathy.
The benefits of L-carnitine include:
- Treatment of primary systemic carnitine deficiency
- Alleviation of signs and symptoms of cardiomyopathy
- Treatment of acute and chronic secondary carnitine deficiency due to inborn errors of metabolism
The side effects of L-carnitine include:
- Gastrointestinal reactions:
- Transient nausea and vomiting
- Abdominal cramps
- Diarrhea
- Musculoskeletal reactions:
- Mild myasthenia (in uremic patients)
- Neurologic reactions:
- Seizures (in patients with or without pre-existing seizure activity)
- Hypersensitivity reactions:
- Rash
- Urticaria
- Facial edema 2
From the Research
Benefits of L-Carnitine
- L-Carnitine contributes to the production of energy and the metabolism of fatty acids 3
- It improves myocardial functionality and metabolism in ischemic heart disease patients, as well as athletic performance in individuals with angina pectoris 3
- L-Carnitine facilitates transport of long-chain fatty acids into the mitochondrial matrix, triggering cardioprotective effects through reduced oxidative stress, inflammation and necrosis of cardiac myocytes 4
- It regulates calcium influx, endothelial integrity, intracellular enzyme release and membrane phospholipid content for sustained cellular homeostasis 4
- L-Carnitine supplementation reduces biomarkers of inflammatory and oxidative stress in patients with coronary artery disease 5
- It may exert beneficial effects on cardiovascular health through attenuating oxidative and inflammatory markers in CAD patients 5
- L-Carnitine can enhance both contractile performance and structural integrity of the cardiac muscle by maintaining efficient energy production and reducing oxidative stress 6
- It seems to have a pivotal role in cardiovascular health due to its energy metabolism, anti-oxidative stress, and endothelial role 6
- L-Carnitine supplementation effectively reduces the inflammatory state by increasing the level of total antioxidant capacity and decreasing the levels of C-reactive protein, interleukin-6, tumor necrosis factor-α, and malondialdehyde in the serum 7
Side Effects of L-Carnitine
- One of the major concerns is that the intestinal metabolism of L-carnitine generates trimethylamine-N-oxide (TMAO), a compound that has been linked with faster atherosclerosis progression 6
- The safety and effectiveness of L-carnitine administration remain an issue for scientific investigation 6
- L-Carnitine supplementation had a significant effect on alanine transaminase (ALT) and aspartate transaminase (AST) in intervention, compared to the placebo group, indicating potential liver effects 7