L-Carnitine and CoQ10 Supplementation: Safety Considerations from Real-World Data with Implications for Health and Sport

Background/Objectives: L-carnitine is a naturally occurring compound involved in energy metabolism, while Coenzyme Q10 (CoQ10) is primarily indicated for CoQ10 deficiency and as adjuvant therapy in chronic heart failure. Both are widely used off-label in sports to enhance performance, reduce fatigue, and improve recovery. Despite their popularity, their safety profiles are mainly derived from pre-marketing studies conducted in deficient or clinical populations, not in athletes. Given this limitation, the present study aimed to evaluate and compare the real-world safety profiles of L-carnitine and CoQ10 using spontaneous reports of adverse drug reactions (ADRs) from the EudraVigilance database. Methods: EudraVigilance, managed by the European Medicines Agency (EMA), collects spontaneous reports of suspected ADRs related to authorized medicines. ADRs associated with L-carnitine and CoQ10 were analyzed and compared at the System Organ Class (SOC) level using reporting odds ratio (ROR) and proportional reporting ratio (PRR). Results: For L-carnitine, the most frequently reported ADRs were gastrointestinal disorders, followed by skin and subcutaneous tissue disorders, general disorders, and nervous system disorders. For CoQ10, the most common ADRs were general disorders and administration site conditions, followed by nervous system disorders, investigations, and gastrointestinal disorders. Comparative analysis (ROR and PRR) showed that CoQ10 was associated with a higher probability of reporting certain ADR categories, particularly blood and lymphatic disorders, musculoskeletal and connective tissue disorders, and nervous system disorders. Conclusions: Although L-carnitine and CoQ10 are widely perceived as safe and commonly used by athletes, real-world data highlight the need for increased awareness of potential risks. Continuous monitoring and periodic reassessment of their benefit–risk profile are essential, especially considering their widespread off-label use.