Onset: 30-60 minutes absorption. Tmax 1-2 hr. Effects (when felt) are slow and tissue-level, not acute neuropharmacological.

Felt effects across dose tiers:

• 50-250 mg/day: Nothing felt — pure B-vitamin coverage. Indistinguishable from placebo subjectively. This is the floor most users notice no change at all.
• 500 mg/day: Some users report very subtle relaxation, mild warmth (NOT the niacin flush — different mechanism; possibly mild GABAergic effect at higher doses or PEA antagonism). No cognitive boost felt.
• 1000-1500 mg/day (high-dose protocol): Reports cluster around (a) deeper sleep, (b) calmer evenings — sometimes described as "background anxiety quieting," (c) improved skin texture over 4-8 weeks, (d) modest joint comfort. Modest but real for the subset of high-dose protocol users. No stimulant feel, no cognitive sharpness, no euphoria.
• 3 g+/day ("schizophrenia megadose"): Sedation. Nausea above 2 g taken acutely. Reports of "fogging" rather than clarity. The mechanism (PARP saturation, methyl-pool depletion, hepatic stress) is exactly what would predict subjective dulling.

Characteristic features:

• This is a slow tissue-level effect, not a felt nootropic. If you expect a noticeable cognitive change within hours, you'll be disappointed.
• Skin effects (texture, redness reduction) typically appear at 4-8 weeks of consistent dosing at 500 mg+, supporting the dermatology use case.
• The "calmer evening" effect at 500-1000 mg is reported in roughly 30-40% of users — not universal, mechanism uncertain (mild GABAergic? methyl-pool downstream effect on neurotransmitter synthesis?).

Honest variability: Roughly 40-50% of users feel literally nothing at supplemental doses. Of the rest, most describe effects as "subtle" rather than "noticeable." This is unlike modafinil or even ashwagandha where the felt effect is more reliable.

• Tolerance buildup: Minimal at the receptor/enzyme level. Niacinamide works as a cofactor substrate, not a receptor ligand — no classical receptor downregulation. NAMPT can theoretically downregulate at chronic high substrate exposure, but clinical relevance is unclear.
• What changes with chronic use: Methylation enzymes (NNMT, nicotinamide N-methyltransferase) upregulate to handle higher NAM throughput — this is the source of the methyl-pool concern. NNMT-induced kynurenine pathway upregulation has been hypothesized to alter mood/anxiety states in long-term high-dose users.
• Recommended cycle: Daily, no cycling at standard doses (50-250 mg). At 500 mg+, some users adopt 5-on/2-off weekly to ease methyl-donor demand and minimize NNMT adaptation. No clinical evidence this matters at moderate doses; mostly belt-and-suspenders.
• Reset protocol: Not applicable in the traditional pharmacological sense. If discontinuing after long-term high-dose use, expect serum 2PY/4PY to normalize within 1-2 weeks (these are short-half-life metabolites). Liver markers normalize within 4-8 weeks of cessation.

Synergistic with

• NMN, NR: Same NAD+ pathway from different entry points. Stacking is not necessary — most NMN/NR ends up as NAM anyway in vivo. Some users layer all three at lower doses each for "pathway saturation"; mechanistically reasonable, evidentially undertested.
• Apigenin: CD38 inhibition (apigenin) + NAD+ supply (niacinamide) is the Sinclair-lab template for sustaining NAD+ levels — slowing breakdown while supplying precursor. The most logical NAD+ stack on paper.
• Pterostilbene + resveratrol (SIRT activators): Theoretically synergistic — SIRT1 activators paired with the SIRT1 substrate (NAD+). Trans-resveratrol has modest human bioavailability; pterostilbene is the better-bioavailable analog. Evidence in humans is limited.
• TMG (trimethylglycine / betaine), methylfolate, methyl-B12: Counterbalance methyl-group demand at chronic high doses. Mandatory pair if going >500 mg/day chronic, especially in MTHFR variants. Cheap insurance.
• Topical retinoids: Topical niacinamide reduces retinoid-induced irritation while complementing the anti-aging mechanism. Standard dermatology pairing (the Discord anecdote in the community-data block reflects this).
• CoQ10, PQQ, l-carnitine (mitochondrial stack): Compound mitochondrial cofactor support. Mechanistically coherent for athletic recovery and post-injury healing.

Avoid stacking with

• Other high-dose niacin (flushing form) in the same window: Redundant pathway saturation + additive 4PY metabolite load.
• Carbidopa, isoniazid: Both interact with B6/B3 metabolism; clinically minor for niacinamide vs niacin but worth flagging.
• Concomitant CYP2E1-induced state (chronic alcohol, certain anti-tubercular drugs): Xu 2025 JAAD review flags 2E1-metabolized co-medications as risk-amplifiers — relevant only for users on isoniazid, disulfiram, or chronic high alcohol.

Neutral / safe co-administration

• All of Dylan's V4-locked stack (creatine, magnesium, vitamin D3/K2, omega-3, citicoline, etc.) — no clinically meaningful interactions.
• Modafinil + niacinamide — neutral. No PK overlap, no clinical signal.

• Statins: Niacin (flushing form) has a rhabdomyolysis interaction with statins via shared CYP3A4 + muscle effects. Niacinamide does NOT share this signal — clinically clean with statins.
• Anticonvulsants (carbamazepine, primidone, phenytoin): May modestly alter B-vitamin pharmacokinetics through hepatic enzyme induction. Clinically minor for niacinamide specifically.
• Diabetes medications (metformin, sulfonylureas, insulin): Monitor glucose at niacinamide doses >1 g/day. The insulin-resistance signal at high doses can affect glycemic control modestly.
• Anticoagulants (warfarin, DOACs): No documented direct interaction. Watch INR if dosing changes during warfarin therapy out of general caution; effect likely minimal.
• Hepatotoxic drugs (acetaminophen high-dose, methotrexate, isoniazid, alcohol): Additive hepatic burden at high NAM doses. Lower threshold for monitoring.
• CYP2E1 substrates (Xu 2025 flag): Concomitant CYP2E1-induced medications may amplify NAM metabolite accumulation. Practical clinical relevance limited but worth noting.
• NAD+-IV protocols: Stacking oral high-dose NAM with NAD+ IV infusions is mechanistically redundant + potentially adds metabolite load. Most clinics' NAD+ IV protocols do not recommend co-administering oral NAM.

• NAMPT (rs61330082, rs10487818): Variants affect rate of NAM → NMN conversion, possibly affecting individual NAD+ response. Not currently actionable in clinical practice.
• NNMT (nicotinamide N-methyltransferase, rs694539, rs1941404): Upregulation associated with metabolic syndrome and obesity in some cohorts. NNMT-active phenotypes may clear NAM faster (lower steady-state) but also produce more 2PY/4PY. This is the most interesting PGx node for the new CV signal.
• MTHFR C677T / A1298C: Variants reduce methyl-folate production → amplify methyl-pool depletion at chronic high-dose NAM. Compound heterozygotes (~7% of caucasians) and homozygotes (~10-15%) should pair NAM dosing with methylated folate (L-5-MTHF) + methyl-B12 if going above 500 mg/day. Relevant for Dylan's pending 23andMe interpretation (June 2026 results).
• PNPLA3 variants (steatohepatitis susceptibility): Theoretically amplify hepatic risk at chronic high-dose NAM. No direct studies in NAM users; mechanistically plausible.
• APOE4: Speculative relevance — APOE4 carriers have lower brain NAD+ + worse mitochondrial function. Whether NAM supplementation provides differential benefit is unclear; one small NR trial signal but not replicated.

Practical takeaway for Dylan: Await 23andMe results (June 2026). Specific gene targets to interpret on receipt: MTHFR C677T/A1298C, NNMT variants if reported, APOE genotype. Default protocol (100-250 mg/day) is below the threshold where these become decisive; if Dylan ever considers a 500 mg+ ONTRAC-style protocol (which is not indicated at his age/profile), MTHFR genotype is the first PGx checkpoint.

Buying notes:

• USP-grade material is the global standard. No counterfeit problem of note in major US/EU vendors.
• "Inositol hexanicotinate" is a slow-release niacin form — not niacinamide; different pharmacology.
• "Nicotinic acid" on the label = flushing niacin, not niacinamide.
• "Nicotinamide" + "niacinamide" + "NAM" are the same compound — labeling varies.

For Dylan: Nutricost or NOW Foods 500 mg caps; split in half for ~250 mg dosing if going the conservative-floor route. ~$8 for 100 caps lasts roughly 200 days at half-cap dosing. Topical: The Ordinary 10% niacinamide if any skin concerns arise — $7, no systemic exposure.

Baseline (before starting, if going >500 mg/day)

• ALT, AST, ALP, GGT — liver panel
• Fasting glucose + HbA1c — insulin resistance baseline
• Homocysteine + folate + B12 — methylation status baseline (critical if MTHFR variant suspected)
• Lipid panel (LDL, HDL, TG, apoB) — cardiovascular baseline
• hsCRP — inflammation baseline (relevant given Hazen 2024 VCAM-1 mechanism)
• 2PY / 4PY plasma levels if available via specialty lab — not yet routine but increasingly accessible
• Creatinine + eGFR — renal function (since NAM metabolites are renally excreted)

During use (>500 mg/day chronic)

• Liver panel quarterly in first year, then annually if stable
• Fasting glucose + HbA1c every 6 months
• Lipid panel + hsCRP annually
• Plasma 2PY/4PY annually if accessible

Post-cycle / on discontinuation

• Repeat ALT/AST + glucose 4-8 weeks after stopping to confirm normalization
• 2PY/4PY normalization expected within 1-2 weeks

For Dylan specifically

• Baseline already planned for June 2026 bloodwork (per project memory). At 100-250 mg/day dose tier, additional NAM-specific monitoring is not warranted. If decision changes to topical-only, no monitoring beyond normal skincare observation.