D-Serine is an amino acid the brain needs for its main learning receptor to work, and levels fall with age. The clearest human results come from psychiatry at higher doses; one short study in older adults improved spatial learning only. Kidney harm appears in rats far above human exposures. No study has run past four months. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum creatinine | 0.6–1.0 mg/dL (women), 0.7–1.2 mg/dL (men), within 10% of personal baseline | Primary signal of proximal tubular injury |
| Estimated glomerular filtration rate (eGFR) | ≥90 mL/min/1.73 m²; below 60 excluded in trials | Sets eligibility and governs total exposure |
| Urinalysis with microscopy (protein, glucose, casts) | Negative for protein, negative for glucose, no granular casts | Detects the tubular pattern seen in rodents |
| Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) | ALT 10–26 U/L (women), 10–33 U/L (men); AST 10–26 U/L (women), 10–30 U/L (men) | Symptom-free elevations occurred at the highest dose |
| Plasma D-Serine | No established target; track change from personal baseline, pre-dose and at two hours | Clinical response tracked the size of the rise |
| Fasting glucose | 75–86 mg/dL | Very high intakes reduced insulin secretion in rodents |
| Blood urea nitrogen (BUN) | 10–16 mg/dL | Separates kidney signal from hydration status |
Cadence: Baseline, 4 weeks, 12 weeks, then every 3–6 months while administration continues, and within a week of any dose increase.