LSD

Taken by mouth, LSD usually begins to act within 20–60 minutes, peaks at around 2–4 hours, and resolves over roughly 8–12 hours. It is active at microgram doses, reflecting its very high potency, and its effects and duration vary with dose and individual factors (Nichols, 2016).

LSD is generally not advised for people with a personal or family history of psychotic disorders (such as schizophrenia) or bipolar disorder, because the experience may trigger or worsen these conditions. Clinical studies routinely screen out such individuals as a basic safety measure (Johnson, Richards & Griffiths, 2008).

• Psychiatric history: personal or family history of schizophrenia, other psychotic disorders, or bipolar I disorder.

• Cardiovascular conditions: LSD raises heart rate and blood pressure, so significant heart disease or uncontrolled high blood pressure increases risk.

• Current medication: see drug interactions below, especially serotonergic psychiatric medicines.

Mixing LSD with other substances can be unpredictable. The most important interactions involve drugs that act on the serotonin system.

• SSRIs and SNRIs (antidepressants): long-term use usually reduces or blunts the effects of LSD. Stopping antidepressants to feel stronger effects is itself risky and should only be considered with medical guidance.
• MAOIs: can unpredictably change the response and are generally considered unsafe to combine.
• Lithium: combining lithium with LSD has been linked to seizures and is considered dangerous; avoid this combination.
• Stimulants: add cardiovascular strain and increase the chance of anxiety or a distressing experience.
• Tricyclic antidepressants: may intensify the effects of LSD.

This list is not exhaustive. Always check an up-to-date interaction resource and speak with a clinician about any prescription medication (NIDA; TripSit drug-combination data).

The most common adverse reaction to LSD is acute psychological distress, often called a 'bad trip'. It can involve intense anxiety, fear, paranoia, confusion, or a frightening sense of losing control. A structured review of hallucinogen safety identified overwhelming distress during the drug's action as the most likely risk of use (Johnson, Richards & Griffiths, 2008).

Because LSD is long-acting (about 8–12 hours), a difficult experience cannot simply be switched off. The likelihood of distress is strongly influenced by 'set and setting' — the person's mindset and their physical and social surroundings — and reassurance in a calm, safe environment often helps. In rare cases distress can lead to dangerous behaviour, such as trying to leave a place of safety.

Serious lasting harm from LSD is uncommon but possible:

• Prolonged psychosis: rarely, LSD can trigger a persistent psychotic reaction, most often in people predisposed to psychotic illness (Johnson, Richards & Griffiths, 2008; Nichols, 2016).

• Hallucinogen Persisting Perception Disorder (HPPD): a rare condition in which visual disturbances — such as trails, halos, or geometric patterns — continue after the drug has worn off. It is most often reported after LSD use and ranges from brief, mild 'flashbacks' to a chronic form. The DSM-5 estimates HPPD-like symptoms in roughly 4% of hallucinogen users, although reliable prevalence data are limited (Halpern, Lerner & Passie, 2018).

• Cardiovascular strain: the rise in heart rate and blood pressure may be hazardous for people with existing heart disease.

• Accidental injury: altered perception and judgement can lead to unsafe behaviour.

Some groups face higher risk and are generally advised not to use LSD:

• People with a personal or family history of psychosis or bipolar disorder, in whom psychedelics may trigger or worsen episodes.

• Adolescents and young adults, whose brains are still developing and who may be more vulnerable to adverse psychological effects.

• Pregnant or breastfeeding people, for whom safety has not been established.

• People in acute psychological crisis or unstable circumstances, where a safe set and setting cannot be ensured.

LSD is not considered physically addictive. It does not produce compulsive drug-seeking or a physical withdrawal syndrome, and classic psychedelics are generally not regarded as drugs of dependence (Johnson, Richards & Griffiths, 2008; Nichols, 2016). Tolerance also builds very quickly: effects diminish sharply if LSD is taken on consecutive days, which discourages frequent use, and tolerance resets after a few days without it.

Fatal overdose from LSD alone is extremely rare, and no reliable lethal dose has been established in humans; deaths associated with LSD are usually due to accidents or dangerous behaviour rather than direct toxicity (Nichols, 2016). Very large doses can cause frightening psychological effects, vomiting, and pronounced increases in heart rate, blood pressure, and body temperature, and accidental mass ingestions have led to serious medical complications. If someone shows signs of a medical emergency — for example chest pain, seizures, a very high temperature, or loss of consciousness — seek emergency medical help immediately.

The scientific evidence for microdosing is still limited and mixed. Many reported benefits come from uncontrolled self-reports, and placebo-controlled studies suggest that expectation (placebo) explains much of the perceived benefit. Reviews also caution that long-term safety has not been established and that frequent low doses could carry unknown cardiovascular risks (Passie, 2019). Microdosing is best regarded as experimental rather than proven.