An amino acid marketed to raise testosterone, but the evidence is inconsistent and often disappointing. Any benefit appears limited to untrained men with lower baseline levels; trained men with normal levels see no gain, and higher intakes can lower testosterone. Inexpensive and well tolerated, yet sleep, training, body composition, and nutrition remain the stronger levers. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Total testosterone | ~500–900 ng/dL | Primary target of the intervention |
| Free testosterone | ~15–25 pg/mL | The biologically active fraction |
| Luteinizing hormone (LH) | ~2–8 mIU/mL | Reflects the brain-to-testes signal the supplement targets |
| Estradiol (E2) | ~20–30 pg/mL | Detects unwanted estrogen lowering |
| Sex hormone-binding globulin (SHBG) | ~20–45 nmol/L | Determines how much testosterone is free vs. bound |
Cadence: Baseline before starting, then at ~2 weeks and again at 4–6 weeks; fasting, morning draw