A naturally occurring amino acid that helps switch on a brain receptor central to learning and memory, which the brain makes less of with age. The strongest human signal — better spatial learning in healthy older adults — rests on one small study, backed by strong animal work. Biologically plausible but lightly tested. (Full Review)

Protocol

Dose

~30–60 mg/kg/day

Commonly ~2 g/day; extrapolated from clinical studies, no validated longevity protocol

Timing

Earlier in the day

Or around cognitively demanding activity; timing not established by trials

Schedule

Split twice daily

Short half-life supports split dosing for stable levels; most trials used daily regimens

Time to effect

Cognitive benefit

Gradual

Uncertain; measured after a defined dosing period, not acutely — do not expect immediate effects

Benefits

Medium: Improved spatial learning and memory in healthy older adults

Low: Symptom improvement in NMDAR-hypofunction states; preservation of synaptic plasticity substrates

Speculative: Broader healthspan and neuroprotection

Contraindications

Significant chronic kidney disease (eGFR <60 mL/min/1.73m²)

Diagnosed or suspected Alzheimer's disease or active neurodegeneration

Pregnancy or breastfeeding

Key Interactions

NMDAR-active prescription drugs (memantine)

DAAO inhibitors (sodium benzoate)

Other glutamatergic and ketamine-class drugs (ketamine, D-cycloserine)

Dextromethorphan (OTC cough suppressant)

Additive supplements (glycine, L-serine, sodium benzoate)

Risk & Side Effects

Medium: Nephrotoxicity

Low: Theoretical excitotoxicity in vulnerable brains; mild gastrointestinal and general tolerability effects

Speculative: Effects on metabolic, cardiac, and movement systems

Monitoring

Marker	Target	Why
eGFR	>90 mL/min/1.73m²	Detects any decline in kidney filtration, the main animal-data safety concern
Serum creatinine	0.6–1.0 mg/dL (sex-dependent)	Direct kidney-clearance marker that feeds eGFR
BUN	10–16 mg/dL	Secondary kidney and hydration marker
Cystatin C	<0.9 mg/L	Kidney filtration marker independent of muscle mass
Blood D-Serine	Individualized vs. baseline	Confirms the dose is actually raising levels, which tracked with cognitive gains

Cadence: Baseline before first dose, then at ~4–8 weeks and every 6–12 months (or sooner if any marker shifts or symptoms arise)

Qualitative Assessment

Subjective memory and recall in daily life
Mental clarity and processing speed
Performance on a repeatable cognitive self-test (e.g., a spatial-learning or working-memory task)
Energy and mood stability
Absence of new urinary symptoms, swelling, or changes in urine output

D-Serine for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment