An essential amino acid, cheap and unusually well characterised for safety: nausea and diarrhoea are the only consistent adverse effects, with a tolerable ceiling around six grams daily. The benefit picture is thinner than its reputation suggests — every effect with human support was shown in people whose diets were short of lysine. The cold-sore claim is genuinely contested. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Plasma lysine (fasting amino-acid panel) | 170–220 µmol/L | Confirms whether intake was limiting before supplementation, and whether it moved after |
| Serum creatinine with estimated glomerular filtration rate (eGFR) | eGFR above 90 mL/min/1.73 m² | The organ that reabsorbs almost all filtered lysine, and the site of the reported tubular injury |
| Urine albumin-to-creatinine ratio | Below 10 mg/g | Earliest detectable sign of glomerular or tubular leak, before filtration rate falls |
| Serum calcium (albumin-corrected) | 9.2–9.8 mg/dL | Lysine raises intestinal calcium absorption and reduces its urinary loss, so both push this upward |
| 24-hour urinary calcium | 100–250 mg/24 h | Detects the calcium retention effect, and flags stone risk when calcium intake is also high |
| Long-term blood-sugar marker (HbA1c) | 4.8–5.3% | Tracks the metabolic signal that the observational lysine-metabolite literature raises |
| Fasting glucose | 75–86 mg/dL | Faster-moving companion to the three-month marker, and the endpoint moved in the prediabetes trial |
| Low-density lipoprotein cholesterol (LDL) | Below 80 mg/dL | Checks the theoretical cholesterol concern raised by older animal work |
| Plasma free carnitine | 30–50 µmol/L | Lysine is carnitine's only precursor, so this is the direct test of the proposed metabolic benefit |
Cadence: Kidney function and urine protein at 4 weeks, again at 3 months, then every 6 to 12 months while use continues. Calcium, glucose and lipids at 3 months and annually thereafter. The purpose-specific endpoint is re-recorded at 3 and 6 months.