From the Guidelines
L-carnitine supplements can cause several side effects, including nausea, vomiting, abdominal cramps, diarrhea, and a "fishy" body odor, particularly at doses of approximately 3 g/day. These side effects are highlighted in the espen micronutrient guideline published in Clinical Nutrition in 2022 1. According to this study, common side effects of L-carnitine supplementation include:
- Nausea
- Vomiting
- Abdominal cramps
- Diarrhea
- A "fishy" body odor Rarer side effects may include muscle weakness in uremic patients and seizures in those with seizure disorders, as noted in the same guideline 1. It is essential to be aware of these potential side effects, especially when considering high doses of L-carnitine supplementation.
The mechanism behind these side effects is not fully understood, but it is thought to be related to L-carnitine's role in fatty acid metabolism, as suggested by a case report that found acute infusion of carnitine resulted in an increased rate of protein oxidation and a reduced rate of fat oxidation 1. To minimize the risk of side effects, it is crucial to follow recommended dosages and consult with a healthcare provider, especially for individuals with pre-existing medical conditions or those taking certain medications.
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. Musculoskeletal Reactions: Mild myasthenia has been described only in uremic patients receiving D,L-carnitine. Neurologic Reactions: Seizures have been reported to occur in patients with or without pre-existing seizure activity receiving either oral or intravenous levocarnitine. Hypersensitivity Reactions: Rash, urticaria, and facial edema have been reported with oral CARNITOR®
The side effects of L-carnitine include:
- Gastrointestinal reactions: nausea, vomiting, abdominal cramps, and diarrhea
- Musculoskeletal reactions: mild myasthenia (in uremic patients)
- Neurologic reactions: seizures
- Hypersensitivity reactions: rash, urticaria, and facial edema 2 Large doses of levocarnitine may also cause diarrhea 2
From the Research
L-Carnitine Side Effects
- The provided studies do not extensively discuss the side effects of L-carnitine supplementation, but some information can be gathered from the texts:
- L-carnitine supplementation can elevate fasting plasma trimethylamine-N-oxide (TMAO) levels, which may be associated with an increased risk of atherosclerosis progression 3.
- High doses of L-carnitine may be required for certain medical conditions, but the optimal dosage and potential side effects are not fully understood 4.
- L-carnitine supplementation may have a positive effect on cardiovascular health by improving energy metabolism, reducing oxidative stress, and maintaining endothelial function, but its safety and effectiveness require further investigation 5.
- Potential benefits of L-carnitine supplementation include:
- It is essential to note that L-carnitine supplementation should be used under medical supervision, especially in patients with underlying medical conditions or those taking other medications, to minimize potential side effects and interactions.
- More research is needed to fully understand the side effects and benefits of L-carnitine supplementation in different populations and medical conditions 6, 4, 7, 3, 5.