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L-Carnitine

Male fertility · Cardiac · Fat metabolism · Exercise recovery

Tier 1 — Strong Evidence

What it is

Essential transporter that shuttles long-chain fatty acids into mitochondria for energy production. Cochrane reviews of male subfertility find carnitine/acetyl-carnitine at 2–4 g/day modestly improves sperm motility and concentration; evidence for clinical pregnancy rates is less consistent. In cardiac patients, meta-analyses show it reduces angina, all-cause mortality after heart attack, and improves exercise capacity in heart failure. Distinct from ALCAR (which crosses the blood-brain barrier for cognitive effects) and carnitine tartrate (faster-absorbing exercise form). Total serum carnitine declines in vegans, dialysis patients, and elderly — these groups benefit most.

Efficacy

4/5

Safety

5/5

Research

4/5

Onset

2/5

Cost

4/5

Drug-int.

4/5

Dose

Male fertility: 2–3 g/day in divided doses. Cardiac support: 2–4 g/day under medical supervision. Athletic: 2 g with carbohydrate pre-exercise.

Time of day & tips

Take with carbohydrate-containing food for best muscle uptake — insulin drives carnitine into cells. Morning doses preferred for energy benefits. Cardiac patients should use under medical supervision. Vegetarians and vegans are commonly deficient.

Cycling

Safe for continuous daily use. Male fertility benefits typically seen within 3–6 months. No cycling needed. Beneficial effects reverse on discontinuation.

Sensitive populations: This supplement's evidence base touches pregnancy, pediatric, or other sensitive populations. Confirm any change with your healthcare provider before use.

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