Per user reports in healthy adults (anecdotal, not clinical):

• Onset: 30-90 min after dose. Effects, when present, are subtle.
• Peak: 1-3 hours. Plasma half-life ~1-2 hours; subjective effect window 2-4 hours.
• Character (when present): Mild, verbal-fluency-like cognitive ease. Some describe "thinking feels less effortful." Not stimulating, not sedating, no euphoria. Many users report nothing at all.
• Most common report: nothing perceptible. This is consistent with the saturated-NMDA-glycine-site mechanism. Sarcosine in a healthy young adult is largely a quiet supplement.
• Side effect tail: Mild GI (loose stool, bloating) at doses >1 g for some users. Mild sleepiness in a small subset (mechanism unclear; possibly secondary to elevated synaptic glycine in brainstem/sleep-relevant nuclei). No reports of activation/anxiety at typical doses.
• In schizophrenia patients (clinical context): the most-reported benefit is improved motivation, reduced flat affect, easier conversation, better cognitive focus — all consistent with the negative-symptom + cognitive-domain trial findings. This is a different experience profile from healthy users, and that gap is the central "why."

• Tolerance buildup: Minimal to none established. Schizophrenia patients show durable response over 6+ months at fixed dose without escalation.
• Recommended cycle: None needed for clinical-indication use. For healthy-adult experimentation, a 4-8 week trial is sufficient to determine null vs subtle positive response; no cycling rationale.
• Reset protocol: N/A.

Synergistic with (in clinical contexts)

• Non-clozapine antipsychotics (risperidone, olanzapine, aripiprazole, etc.) — well-evidenced clinical synergy in schizophrenia. Not relevant to Dylan.
• D-serine, glycine high-dose — overlapping mechanism (all raise NMDA glycine-site activation). Not commonly stacked clinically; sarcosine is the more efficient single agent. Not relevant to Dylan.
• N-acetyl-cysteine (NAC) — mechanistically complementary in schizophrenia (NAC modulates glutamate release via cystine-glutamate antiporter; sarcosine enhances NMDA receptor function). Some clinical interest in the combination. For Dylan: NAC is in V4 stack, but the rationale is GSH/oxidative-stress/respiratory, not NMDA modulation; co-administration safety is fine but no synergy meaningful for Dylan's profile.
• Memantine — mechanistically opposed (memantine is an NMDA antagonist). Rarely co-prescribed; mechanistic conflict. Not relevant.

Avoid stacking with

• Clozapine — the canonical "avoid" interaction. Multiple trials and meta-analyses show sarcosine does not augment clozapine and may antagonize clozapine's effect on negative symptoms. Mechanism is debated — possibly because clozapine itself has direct effects on NMDA glycine-site signaling that occlude further sarcosine modulation, or via a glycine-cycle saturation effect. The empirical finding is robust enough that sarcosine is contraindicated as a clozapine adjunct in clinical practice. Not Dylan-relevant, but the most important interaction to know.
• NMDA antagonists (memantine, ketamine, dextromethorphan at high doses, PCP analogs) — mechanistic opposition. Don't co-administer for therapeutic purposes; recreational/research interactions unstudied.
• MAOIs — no documented interaction, but caution warranted in any glutamatergic-modulator combination with monoamine oxidase inhibition.

Neutral / safe co-administration

• Caffeine, modafinil, racetams, ALCAR, alpha-GPC, magnesium, l-theanine, l-tryptophan, glycine (modest mechanistic redundancy but not antagonistic), all standard nootropic/supplement stack components.
• All Dylan's V4 stack components.
• All planned V5 additions.

Limited PGx data of practical significance for sarcosine:

• SLC6A9 (GlyT1) variants — affect transporter function. Loss-of-function SLC6A9 variants cause glycine encephalopathy in compound heterozygotes. Common SLC6A9 SNPs are linked to schizophrenia susceptibility in some studies and theoretically alter sarcosine's potency at the transporter, but no actionable PGx-sarcosine dose recommendation exists.
• GRIN1 / GRIN2A / GRIN2B (NMDA receptor subunits) — variants affect NMDA receptor function broadly. Theoretically modulate sarcosine response; no clinical translation yet.
• SARDH (sarcosine dehydrogenase) variants — affect sarcosine clearance. Loss-of-function causes elevated baseline sarcosine (sarcosinemia, generally benign). No actionable supplementation guidance.
• GLDC, GCSH, AMT (glycine cleavage system) — affect glycine metabolism upstream of sarcosine. Severe variants cause nonketotic hyperglycinemia (neonatal lethal); heterozygous carriers may have mildly elevated baseline glycine. No actionable PGx.
• 23andMe relevance for Dylan (June 2026 results): essentially none. No actionable sarcosine-specific PGx finding expected.

Recommended for Dylan: Don't source. No indication. If trialed despite this for curiosity, BulkSupplements powder is the cheapest entry point (~$15-20 for several months of supply at 1 g/day).

Cost-of-entry context: $15-30/month puts sarcosine in the same cost band as glycine, l-tryptophan, NAC, ALCAR — cheap. This is not a "skip because expensive" call; it's a "skip because no expected effect in Dylan's archetype" call.

Baseline (only if trialing)

• Subjective cognitive diary — verbal fluency, working-memory ease, motivation/drive (1-10 scales) for 7-14 days before starting.
• Plasma sarcosine and glycine (specialty amino acid panel) — useful for mechanistic curiosity, not for routine dosing.
• Hs-CRP — only relevant if neuroinflammation is the suspected modifier; not generally indicated.

During use

• Subjective cognitive measures weekly for 4-8 weeks.
• If response is null at 4 weeks at 1-2 g/day, drop the trial. No deeper biomarker work justified.

Post-cycle

• N/A — no cycling needed.