Psychoactive Drugs and Neurochemistry

3_Psychoactive Drugs and Neurochemistry
Psychoactive Drugs and Neurochemistry
What is a psychoactive drug?
Psychoactive drugs are chemicals that may affect mood, behaviour,
mental processes, and conscious experience.
They do this primarily by acting on the central nervous system, thereby
altering brain function. Most psychoactive drugs act by altering
neurotransmission in at least one of four ways:
1. By altering the amount of neurotransmitter released by a neuron
2. By mimicking the neuron at the receptor site
3. By blocking receptors for certain neurotransmitters
4. By blocking reuptake of the neurotransmitter from the synapse
There are four general categories of Psychoactive
Depressants: e.g. ethyl alcohol, tranquilisers, barbiturates,
These are a class of drug whose action serves to depress central nervous
system activity. Their principal effect is to reduce levels of physiological
arousal, and help us relax, generating a sense of well-being. They are
also the substances most likely to create symptoms of tolerance,
withdrawal, and physical dependence.
Alcohol, easily the most used depressant, tends to initially produce a
feeling of well-being and of stimulation, as the inhibitory centres in the
brain become depressed. Typical features of intoxication might be:
impaired motor function, i.e. staggering or slurred speech, confusion,
3_Psychoactive Drugs and Neurochemistry
slower reaction time, impaired executive decision making, and possibly
impaired vision and hearing.
Stimulants: e.g. nicotine, caffeine, amphetamine, cocaine: These are the
most commonly consumed psychoactive substances, and their effect is to
increase behavioural activity, engendering a sense of alertness and
Narcotic opiates: opium, morphine, heroin, codeine: This is a class of
drugs distinguished by their sleep-inducing and pain-relieving, or
analgesic, effects. The effects of narcotic opiates on consciousness are
complex. Drowsy, cloudy, feelings occur because opiates depress the
activity of parts of the cerebral cortex. But they also produce excitation in
other parts, leading users to experience a sense of euphoria. The term
opioid refers not only to naturally occurring narcotics, but also to
synthetic variations such as methadone or pethidine. (Barlow, 2005,
Psychedelics and Hallucinogens: e.g. marijuana, LSD, psilocybin, PCP,
mescaline, Magic MushroomsThese alter consciousness by dramatically
changing emotions, perceptions, and cognitions; sight, sound, feelings,
and taste will be distorted. The risk of developing either a physical or
psychological dependence on these substances is considered to be low
Classification of Psychoactive Substances
Psychoactive drugs are usually classified in terms of their function:
Their effect on the nervous system
Intended therapeutic use
3_Psychoactive Drugs and Neurochemistry
Classification in terms of function (and legal status) permits a multidimensional approach to the definition of any given mood-altering
substance. Heroin, for example, would be classified as follows:
1. Legal status: Illicit
2. Effect on central nervous system: Depressant
3. Therapeutic Use: Analgesic/ Euphoriate/ Antidiarrhoeal
4. Origin: Opiate
5. Chemistry: Opiate