Lysergide (LSD)
Drugs of abuse
Drugs of abuse
A very potent semi-synthetic psychedelic that activates serotonin 5-HT2A receptors; it alters perception for many hours but rarely causes toxic death.
Also called: Lysergic acid diethylamide, Acid
Quick facts
- Group
- Drugs of abuse
- Target
- Serotonin 5-HT2A receptor (also other 5-HT and dopamine receptors)
- Used for
- No approved medical use · Clinical relevance
- Key effects
- Mydriasis · Nausea · Intense emotions
- Monitor
- Heart rate · Mental state and risk of self-harm
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows LSD bound to the human 5-HT2A receptor (crystal structure).
LSD is an agonist at serotonin 5-HT2A receptors on cortical pyramidal neurons, especially in the prefrontal cortex. Activating these Gq-coupled receptors disturbs how the cortex filters and integrates sensory input, which produces visual distortions, synaesthesia and altered sense of self. It also binds other serotonin and dopamine receptors, which adds to its effects. Tolerance develops after a few daily doses, without a withdrawal syndrome.
- LSD binds 5-HT2A receptors on cortical neurons
- Gq signalling changes cortical filtering of sensory input
- Visual distortions, intense emotions, altered self
- Tolerance after repeated days; no withdrawal
Indications
- No approved medical use; psychedelics are being studied in research settings
- Clinical relevance: hallucinogen intoxication («bad trip») and hallucinogen persisting perception disorder Hallucinogen and dissociative drug intoxication (LSD, PCP, ketamine) →
Adverse effects
Common
- Mydriasis, tachycardia, raised blood pressure and flushing
- Nausea, headache and hyperreflexia
- Intense emotions, from elation to fear and panic
- Visual distortions and loss of time sense
Contraindications
- No medical use outside research
- Psychotic illness or vulnerability to it, which it can unmask
- Heart disease (raised blood pressure and heart rate)
Key interactions
- SSRIs, MAOIs and other serotonergic drugs
- Serotonin syndrome risk
- Stimulants and cannabis
- More anxiety, tachycardia and risk of a frightening experience; cannabis can trigger flashbacks
What is monitored
- Heart rate, blood pressure and temperature
- Mental state and risk of self-harm or injury
- Look for co-ingested drugs and other causes of delirium
Pregnancy and breastfeeding
No safety data in pregnancy; use is discouraged.
Nursing care
- Use calm reassurance («talking down») in a quiet, dim, safe room
- Stay with the patient; remove objects that could cause injury
- Benzodiazepines are used for severe agitation; antipsychotics can worsen the experience
- Arrange psychiatric follow-up if psychosis persists
Pharmacokinetics
- Absorption
- Rapid by mouth, usually from impregnated paper squares («blotters») held in the mouth
- Metabolism
- Liver
- Onset and duration
- Effects begin in under an hour, peak at two to four hours and fade over six to eight hours
Test yourself
Think of the answer, then tap the question to see it.
Which receptor mediates the hallucinogenic effect of LSD?
The serotonin 5-HT2A receptor, a Gq-coupled receptor on cortical neurons.
What is the first-choice management of a «bad trip»?
Calm reassurance in a safe, quiet setting; benzodiazepines for severe agitation.
What is hallucinogen persisting perception disorder?
Recurrent visual disturbances (flashes of colour, trails, afterimages) long after hallucinogen use.
Connections
← Back to the class: Drugs of abuse
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Psychedelic and Dissociative Drugs (National Institute on Drug Abuse (NIDA), 2026); Drugs A to Z (National Institute on Drug Abuse (NIDA), 2025).
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Representative model, for educational purposes only.