L-Carnitine for Male Infertility
L-carnitine consistently improves sperm motility, morphology, and DNA integrity in men with idiopathic infertility, but it has not been shown to raise clinical pregnancy or live-birth rates. Treat it as a modest sperm-quality aid, not a proven fertility treatment.
Why this grade7-layer evidence engine
This earns a Preliminary (B) grade because the evidence is consistent on surrogate markers but empty on outcomes that matter. Multiple systematic reviews and meta-analyses (PMID 35128424, PMID 34871624, PMID 40350672) agree that L-carnitine improves sperm motility by roughly 5 to 11 percent, along with morphology and DNA fragmentation. These findings are reproducible, but GRADE certainty was rated low to very low.
The gap is the clinical endpoint. The same reviews found no significant improvement in pregnancy: PMID 35128424 reported a pregnancy rate ratio of 1.03 (95% CI 0.54 to 1.96), and PMID 34871624 found 16.2% versus 11.2% (p=0.05, not significant). Live-birth data are largely absent, and most trials (including RCTs PMID 30873633 and PMID 35856361) used combination formulas, making it hard to credit L-carnitine alone.
Authorities are split and cautious. The FDA treats it only as a nutrient supplement, and EFSA rejected the claim that it supports normal sperm production. Mayo Clinic says the acetyl-L-carnitine combination did not raise sperm production or motility, and urology guidance finds the evidence too weak to recommend it; Cleveland Clinic is more favorable. A drug-interaction warning (warfarin, levothyroxine, valproate) also applies.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.647
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (2 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status