When to Stop

• HPPD (Hallucinogen Persisting Perception Disorder) — visual snow, tracers, palinopsia, geometric afterimages persisting after the trip ends. Estimated incidence 1-4% of psychedelic users develop some persistent visual phenomenon; clinically significant HPPD (HPPD-2, distressing, persistent) is rarer (<1%). Risk factors: heavy use, polysubstance use, anxiety predisposition, possibly genetic visual cortex vulnerability. Treatment options limited (clonidine, lamotrigine, levetiracetam tried; SSRIs may worsen). A meaningful permanent risk for any psychedelic use.
• Psychosis precipitation in vulnerable individuals — undiagnosed schizophrenia, bipolar, or schizoaffective vulnerability can be unmasked by LSD. Risk concentrated in family-history-positive individuals or prodromal-stage adolescents/young adults. a user in this archetype is in the demographic age window where prodromal psychosis can emerge (peak schizophrenia onset 18-25 in males) — even without family history, this is a non-trivial baseline risk that Schedule I psychedelic use can trigger.
• Suicidal ideation, dysphoric afterglow — minority of users experience prolonged negative mood post-trip ("come-down depression"); rare but documented.
• Persistent perceptual or anxiety changes beyond HPPD — depersonalization/derealization disorder, "trip stuck" phenomena, sometimes resolving over weeks-months.
• Cardiac valvulopathy at chronic microdosing — theoretical. This is the single most-debated chronic-use risk and deserves elaboration:
• LSD is a 5-HT2B partial agonist. 5-HT2B activation on cardiac valve fibroblasts drives fibroblast proliferation → valve thickening → regurgitation/stenosis ("valvulopathy").
• This is the same mechanism that retired fenfluramine (Fen-Phen, 1997) and pergolide (Permax, 2007). Both were used at much higher chronic exposures than microdose LSD.
• Acute / occasional macrodose use does not produce meaningful cumulative 5-HT2B exposure; risk is theoretical and not observed in occasional users.
• Chronic microdose protocols (every 3 days for months/years) produce cumulative 5-HT2B exposure. Theoretical concern is real; empirical confirmation is absent because the long-term-microdose user population is small, recent, and largely uncharacterized epidemiologically.
• No published case series of microdose-induced valvulopathy as of 2026. This is a low-base-rate signal that would take large populations + decades to confirm or refute. Some experts (David Nichols, others) have flagged this as a concern in the Mindmed Phase 3 / clinical translation context.
• Practical implication: if a person was going to chronic-microdose LSD, baseline + annual echocardiogram would be the responsible monitoring approach. Most microdosers don't do this.
• Seizures — rare at therapeutic-equivalent doses, but well-documented with lithium co-administration (see Drug Interactions). Sub-clinical EEG changes have been reported.
• Acute toxicity death — extraordinarily rare with pure LSD (LD50 in humans estimated >12,000 µg, requiring hundreds of typical doses). Most "LSD deaths" are from NBOMe substitution or polysubstance combinations or behavior-related (jumped from heights, etc.). LSD itself is one of the lower-acute-toxicity drugs in the recreational pharmacopeia.
• Acute trip (8-12 hr): continuous, ideally with sober sitter
• First week post-dose: afterglow phase — most users feel positive; minority experience low mood / dysphoria
• First month post-first-dose: HPPD typically presents within first 1-30 days if it's going to present at all
• Chronic microdose use beyond 6 months: valvulopathy theoretical concern starts to apply; no clinical monitoring guideline established
• Family history schizophrenia / bipolar I: lifelong watch — psychedelics may unmask vulnerabilities at any point