Onset of effects, by domain (gray-market injectable; Scenesse implant differs):

• Nausea: uncommon at 250-500 mcg dose, mild when present, typically only on first 1-3 injections; resolves with continued dosing. Substantially less than MTII's near-universal early-loading nausea. Some users report no nausea ever.
• Facial flushing: present but less intense than MTII; lasts 1-2 hours post-injection vs. MTII's 2-4 hours. Not all users experience it.
• Tanning: slower than MTII. First visible darkening at 2-4 weeks of daily loading dose with paired UV exposure. Plateau at 6-10 weeks. Some users describe it as "barely noticeable in the first month, then gradually obvious." Pattern: more uniform across body, less concentrated on existing freckles/moles than MTII.
• Mole/freckle darkening: present but less pronounced than MTII. Existing nevi do darken, but less aggressively. New nevus formation is reported but at lower frequency than MTII case reports.
• Spontaneous erections: not reported. This is the cleanest distinction from MTII. The MC1R-preferential profile means MC4R-driven sexual arousal pathway isn't substantially activated at therapeutic dose. Some users specifically choose MTI over MTII for this reason (don't want the libido effect).
• Appetite suppression: mild and inconsistent. Some users notice slight reduction first day of dosing; most don't notice meaningful change. For an combat athlete eating to support training, this is the right side-effect profile — MTII's chronic appetite suppression conflicts with training nutrition; MTI's mild, transient effect doesn't.
• Yawning + stretching: mild "yawning syndrome" reported by some users, less prominent than MTII.

Characteristic effects pattern:

• "Slower tan, cleaner profile" — the dominant peptide-community framing of MTI vs. MTII. Users wanting fast results pick MTII; users wanting a tolerable protocol pick MTI.
• "More like a sun tan, less like a peptide tan" — uniform pigmentation distribution, less mole-and-freckle concentration.
• "Almost no side effects" common report at maintenance dose. This is part of the concern — users underestimate the still-real long-term unknowns.

Honest variability:

• MC1R LOF variants (red-hair, fair Celtic/Nordic phenotype) get markedly less tanning response from MTI just as from MTII. Receptor-level limitation, not pharmacology issue. the user's Nordic/British ancestry suggests intermediate risk for MC1R variants — 23andMe results (June 2026) will inform.
• Phototype dependency: Phototype II-III (this-archetype: fair, tans with effort) is the optimal MTI use case — enough functional MC1R to respond, enough fair skin baseline that the effect is visible. Phototype I (red hair, never tans) gets minimal response. Phototype V-VI gets visible darkening but no clear benefit case for non-medical use.
• Dose-response is gentler than MTII — 250 vs. 500 mcg makes less difference than the equivalent MTII dose change. This is part of the cleaner profile.

• Tolerance to therapeutic effect (tanning): Modest. Most users hit pigmentation plateau at 6-10 weeks and maintain on 1-3×/week dosing. Stopping for several weeks and restarting still works.
• Tolerance to side effects: Develops over 7-14 days for the mild GI/flushing effects.
• Cycling: No formal cycling pattern in gray-market literature. Common pattern: "load → maintenance → seasonal break (winter, low UV anyway)." Some users dose continuously for years; long-term safety in this pattern is unstudied at gray-market doses (Scenesse 12-year EPP registry is the closest, but at controlled-release implant exposure not bolus injectable exposure).
• Reset / discontinuation: Pigmentation gradually fades over 2-4 months without dosing + UV. New nevi formed during use generally do not regress.

Synergistic with

• Astaxanthin (V5 candidate for users in this archetype): independent photoprotective mechanism (ROS scavenging in skin) layered with MTI's eumelanin upregulation. Genuinely complementary photoprotection stack.
• Topical broad-spectrum sunscreen for high-UV-index days: MTI gives ~SPF 2-4 baseline; not a sunscreen substitute. For the user's outdoor MMA seasons or summer travel, sunscreen layered on MTI is the right combination.
• Vitamin D3 + K2 (V4 stack): continue regardless. Increased eumelanin slightly reduces UVB-driven D3 synthesis per unit exposure, so D3 supplementation matters more, not less, on MTI.

Avoid stacking with

• MTII — receptor saturation + additive side effects + same pathway. Pick one melanocortin tool.
• Bremelanotide (PT-141) chronic use — same family, redundant; if PT-141 is used PRN for sexual function, that's separable.
• Other photosensitizing drugs (some antibiotics like doxycycline, some retinoids) — MTI doesn't directly interact, but the compound use case (more UV exposure with less burn) compounds photosensitization risk in the wrong direction.

Neutral / safe co-administration

• the user's V stack base stack — no documented interaction with omega-3, citicoline, magnesium, NAC, PS, curcumin, rhodiola, theanine, glycine, D3+K2, beta-alanine, vitamin C.
• Modafinil (V5 onboarding) — no documented direct interaction. Different pharmacology entirely.
• BPC-157 + TB-500 (the user's elbow protocol) — no documented interaction. Different peptide families, different receptors.
• Creatine — no interaction.

• Not metabolized via CYP enzymes (peptide; cleared by peptidases + renal excretion). No CYP induction or inhibition.
• Hormonal contraceptives: no documented interaction.
• Antihypertensives: unstudied; transient mild BP effects rarely reported.
• Photosensitizing drugs: no direct pharmacokinetic interaction, but use-case interaction (additional UV exposure on MTI compounds photosensitization risk).
• GLP-1 agonists (retatrutide, semaglutide, tirzepatide): mild theoretical additive nausea on first dose. Less concerning than MTII pairing.

• MC1R variants (rs1805007, rs1805008, rs1805009 + ~80 other low-frequency variants): Loss-of-function variants are the canonical "red hair / fair skin / freckles / poor tanning" SNPs. People with two LOF MC1R alleles produce predominantly pheomelanin regardless of melanocortin signaling input. MTI cannot rescue MC1R loss-of-function — the receptor can't drive eumelanin synthesis if the receptor itself is defective. Practical: red-haired Celtic/Irish phenotype users get minimal tanning benefit from MTI while still getting full side-effect exposure (such as it is).
• For the user (23andMe results June 2026): MC1R genotype is the gating biomarker. Nordic/British ancestry has ~10-20% MC1R variant carrier rate. If 23andMe shows two LOF MC1R variants: MTI is mechanistically dead — skip permanent. If one LOF variant (heterozygous): partial response expected, magnitude unstudied. If zero variants: full tanning + photoprotection response expected. This is one of the few compounds where 23andMe results meaningfully gate the verdict.
• MC4R variants: Affect appetite/satiety/sexual response magnitude. Less relevant for MTI's MC1R-preferential profile than for MTII's non-selective profile.
• Family history of melanoma / dysplastic nevus syndrome / FAMMM: If positive (TBD — the user's family history thread is open), MTI shifts to SKIP. Mechanistic stimulation of melanocyte activity in genetically pre-disposed individuals is wrong-direction risk.

COA / vendor reality check

• The "research chemical" framing is a regulatory loophole, not quality assurance. Same critique as MTII. As Gerstman 2024 documents, most US "peptide brands" are repackagers of Chinese bulk peptide. Some publish HPLC + mass spec COAs; most don't.
• MTI's lower side-effect profile means contamination/under-dosing is harder to detect by user. With MTII, severe nausea or unexpected priapism flags vendor quality issues; with MTI, minimal effects could mean either "working as expected" or "vial is half-strength or contaminated." This is a subtle reliability concern specific to cleaner peptides.

Baseline (before starting if using)

• MC1R genotype (23andMe gives rs1805007, rs1805008, rs1805009 + others).
• Total-body skin photography (dermatology-grade or smartphone with consistent lighting, mapped to anatomic regions).
• Dermoscopy of any nevus >2 mm or with prior atypia.
• Family history of melanoma or dysplastic nevus syndrome documented.
• Blood pressure baseline.
• Basic metabolic panel.
• 25(OH) vitamin D — already on the user's June 2026 panel via V4 5000 IU D3 dose calibration.

During use

• Symptom log first 2 weeks: any GI/flushing tolerance, headache.
• Monthly skin self-exam comparing to baseline photos.
• 3-month dermatology follow-up for full-body re-exam, then every 6 months.

Post-cycle (if cycled)

• Repeat dermatology exam at 3 months post-cessation to document any nevus changes that emerged late.
• 25(OH) vitamin D re-check if D3 dose needs recalibration after pigmentation increase.

• mtii.md — Sister cyclic peptide. Non-selective vs. MTI's MC1R-preferential. More aggressive side-effect profile (priapism, severe nausea, more mole/freckle hyperpigmentation). For the user: SKIP-FOR-NOW (HIGH confidence). MTI is the cleaner, FDA-approved-indication-having alternative.
• bremelanotide.md — MC4-leaning FDA-approved metabolite of MTII. For sexual function indication. Different use case than MTI.
• vitamin-d3.md (if added) — MTI doesn't substitute. Eumelanin upregulation modestly reduces UVB-driven D synthesis. Continue 5000 IU D3 + K2 regardless.
• astaxanthin.md (V5 candidate) — Independent photoprotection via ROS scavenging. Synergistic stack with MTI for outdoor athlete photoprotection.
• kpv.md (related — α-MSH C-terminal tripeptide, anti-inflammatory rather than melanogenic) — Different MSH-derived therapeutic vector. Not interchangeable.
• ghk-cu.md (related — copper peptide for skin) — Cosmetic-skin family of peptides; different mechanism (matrix remodeling, anti-aging) than MTI's pigmentation.
• (Future: setmelanotide.md — MC4-selective FDA-approved for syndromic obesity, cleaner selectivity example.)