L-Carnitine

• L-Carnitine is NOT a peptide — it's a small amino-acid derivative (~161 Da), synthesized in the body from lysine and methionine, essential for transporting long-chain fatty acids into mitochondria for energy production.
• It is genuinely FDA-approved (as Carnitor) for primary and secondary carnitine deficiency and for dialysis patients — one of the few approved items in this library — and has the strongest peer-reviewed evidence base here.
• Injectable delivery gives ~100% bioavailability vs ~14–18% oral, and bypasses the gut-microbiome conversion to TMAO that oral dosing triggers.
• Two clinically meaningful interactions to flag: it may enhance anticoagulants (warfarin/acenocoumarol) and may inhibit thyroid hormone action — worth real attention, unlike most 'interactions' in this space.

L-Carnitine (levocarnitine) is a naturally occurring compound central to fat metabolism: it carries long-chain fatty acids into the mitochondria where they're burned for energy. It's concentrated in high-energy tissues — heart, brain, skeletal muscle — and the body makes its own, so true deficiency is uncommon outside specific medical conditions.

Unusually for this site, the injectable form is an FDA-approved drug (Carnitor) with a large clinical-trial base. Everything below is research/clinical context, not medical guidance.

L-Carnitine is a small molecule (~161 Da), not a peptide — it's a quaternary ammonium compound derived from the amino acids lysine and methionine. Several forms exist for different uses: acetyl-L-carnitine (ALCAR) is favored for cognitive research, L-carnitine L-tartrate (LCLT) for exercise recovery, and propionyl-L-carnitine (PLC) for cardiovascular applications.

The reason injection is used at all is bioavailability: oral L-carnitine is only ~14–18% absorbed and a chunk of it is converted by gut bacteria to TMAO (a metabolite of cardiovascular interest). Injectable L-carnitine reaches ~100% bioavailability and skips that gut step entirely.

L-Carnitine is the obligatory shuttle for the 'carnitine shuttle': it binds long-chain fatty acids and ferries them across the inner mitochondrial membrane so they can undergo beta-oxidation (fat burning). Without adequate carnitine, fat can't be efficiently used for energy. It also helps buffer the mitochondrial acyl-CoA pool, supports energy production in the heart and muscle, and has antioxidant and ammonia-lowering effects.

Approved medical dosing is weight-based; performance protocols are lower and intermittent. Figures below are clinical/research context, not guidance.

• Primary carnitine deficiency: ~50 mg/kg/day, divided or as continuous IV
• Hemodialysis: ~10–20 mg/kg post-dialysis by slow IV push (FDA-approved use)
• Fat metabolism / performance: ~500–1,500 mg, 1–3× weekly, subcutaneous or IM
• Critical illness (research): up to ~300 mg/kg/day IV
• No cycling is needed therapeutically; performance protocols often run 8–12 weeks

• Usually supplied as a pre-mixed sterile solution — no reconstitution. Solution is clear and colorless (a slight yellow may be within manufacturer spec).
• IV can be given as a slow bolus (over ≥2–3 minutes) or diluted in saline; IM/subcutaneous for performance use.
• Store unopened at room temperature; refrigerate after opening. Discard if cloudy, particulate, or the seal is damaged.

L-Carnitine has a well-established safety profile (it's FDA-approved). The most common effects are mild injection-site reactions and, at high doses, a fishy body odor (from trimethylamine production). The interactions matter more than the side effects: use caution in hypothyroidism (it may inhibit thyroid hormone action) and monitor patients on anticoagulants (it may enhance warfarin/acenocoumarol effect). Renal patients are monitored for TMA/TMAO accumulation.

• Weight-loss meta-analysis (2020, 37 RCTs, 2,292 participants): modest but significant reductions — about −1.21 kg body weight and −2.08 kg fat mass, with the effect maxing out around ~2,000 mg/day.
• Cardiovascular secondary prevention (2013, Mayo Clinic meta-analysis, 13 trials, 3,629 patients): associated with ~27% lower all-cause mortality, ~65% fewer ventricular arrhythmias, and ~40% less angina after myocardial infarction.
• Exercise recovery, L-carnitine L-tartrate (2021 RCT, 73 participants, 2 g/day, 5 weeks): improved recovery and soreness and lower creatine kinase vs placebo.

Injectable L-carnitine (Carnitor / levocarnitine) is an FDA-approved prescription drug for carnitine deficiency and dialysis-related deficiency. Oral L-carnitine is sold as a dietary supplement. It is not prohibited in sport.

All citations link to the original source (PubMed, journal site, or regulatory filing). Independent research database — no vendor influence on what's cited.