A useful classification of (some) psychoactive drugs
A medical and pharmacological perspective
A useful classification of (some) psychoactive drugs
The term psychoactive drug typically refers to drugs which reliably alter human’s perception, thought, mood, sensations and ability to test reality. Physicians and basic scientists who regularly study the effects of psychoactive drugs in humans and experimental animals would agree that drugs like LSD, mescaline, ketamine, PCP, scopolamine, salvinorin A and ibogaine all cause perceptual distortions or frank hallucinations.
Typically, these drugs are subdivided as follows:
· Psychedelics: drugs with LSD-like effects in humans via 5-HT2A receptor activation
o Orientation to person, place and time typically intact
· Dissociative agents: includes classes of drugs like ketamine and PCP which are NMDA receptor antagonists.
o Reality testing can be impaired
o Impairs memory
o Impairs orientation to person, place and time
· Delirants: drugs which cause a delirium (disorientation to space and time with altered sensorium). Includes mainly anticholinergics (scopolamine)
o Reality testing impaired
o Cognition impaired
o Disorientation to person, place and time
o Waxing and waning consciousness
· Onerigens: drugs which cause a dream-like state
o Reality testing impaired
o Disorientation to space, time and person
o Intact sensorium
A useful classification scheme is shown in the figure below:
As can be seen, the classification system is a pharmacological and medical one that is useful for physicians especially in understanding how particular psychoactive drugs mediate their actions. As well the classification scheme provides insights into potential treatments for untoward side-effects as follows:
To abort a psychedelic experience a 5-HT2A antagonist (e.g. ketanserin or pimavanserin) might be used
To treat anticholinergic delirium physostigmine a cholinergic agonist is used.
To treat PCP psychosis benzodiazepines are typically used along with supportive treatment (BZPs are GABA-positive allosteric modulators).
To reverse the effects of salvinorin A, naltrexone (a pan opioid antagonist) may be used. It is unknown what effects an opioid antagonist has on the effects of ibogaine in humans
As shown below, profiling exemplar compounds at a large number of human CNS molecular targets shows that:
Salvinorin A is selective for the k-opioid receptor
LSD has a complex polypharmacology
Ketamine (at concentrations <10 uM) is selective for NMDA receptors
