When to Stop

• UVA-induced DNA damage — Wenz et al. 2013 (RSC Org Biomol Chem, "Mechanisms of DNA damage by photoexcited 9-methyl-β-carbolines") demonstrated that 9-methyl-β-carbolines under UVA irradiation in cellular assays produce 8-oxo-7,8-dihydroguanine (a mutagenic oxidized purine), single-strand DNA breaks, abasic sites, micronucleus formation, and decreased cell proliferation. The DNA damage pattern is type-I photochemical (radical-mediated) and predominantly oxidized-purine-skewed. Translation to whole-organism cancer risk in chronic biohacker users is unquantified — the effect is documented in cell models, has not been studied in human skin in vivo, but the mechanism is concerning enough that "stay out of strong sun while dosing and for 3-7 days after stopping" is the consensus biohacker recommendation. For a combat athlete with outdoor training exposure, this is non-trivial.
• Tyramine pressor reaction (theoretical, MAO-A inhibition mechanism) — IC50 1 μM for MAO-A means at sufficient plasma concentration the molecule could behave like a partial MAO-A inhibitor. Tyramine-rich foods (aged cheese, fermented soy, tap beer, cured meat) could in principle produce hypertensive reactions. No documented human cases, but the mechanism warrants dietary awareness on chronic dosing.
• Serotonin syndrome (theoretical) — combining 9-Me-BC with serotonergic drugs (SSRIs, SNRIs, tramadol, MDMA, high-dose DXM, St. John's Wort) is theoretically dangerous. No documented human cases, but the MAO-A inhibition arm makes the textbook risk real.
• α-synuclein/dopaminergic effects in chronic high-dose use — the Parkinson's-relevant dimethyl-β-carboline congeners are dopaminergic neurotoxins. 9-methyl appears protective in the published literature, but very-long-term effects in humans are entirely uncharacterized.
• Hepatic effects (theoretical) — β-carboline class includes some hepatotoxic compounds; 9-Me-BC liver-toxicity profile in humans is uncharacterized. ALT/AST monitoring at 4-week intervals if cycling repeatedly is prudent.
• Photosensitivity: entire dosing period + 3-7 days post-discontinuation. Avoid prolonged direct UV exposure. SPF 50+ on uncovered skin if outdoor exposure unavoidable. This is the most concrete and most-commonly-violated safety guidance.
• First 2 weeks: monitor mood (anxiety/aggression flag), GI tolerance, photosensitivity reaction.
• Month 1+ chronic use: ALT/AST, BP, mood-self-report.