Neurotransmitter

A neurotransmitter is a chemical signal that neurons use to communicate across the synapse — the narrow gap between two nerve cells. When an electrical impulse reaches the end of a neuron, it triggers the release of neurotransmitter molecules into that gap, where they bind to receptors on the receiving cell and either excite it or inhibit it.

The nervous system uses dozens of distinct neurotransmitters, each with its own receptors, brain circuits, and functional role. The most pharmacologically significant include dopamine, serotonin, norepinephrine, glutamate, GABA, acetylcholine, and the endogenous opioids — each tied to different aspects of mood, cognition, arousal, pain, and perception.

How it works · its role

Neurotransmitter signalling follows a consistent cycle. A neuron synthesises the molecule and stores it in small packets near the nerve terminal, releasing it in response to electrical activity. Once in the synapse, it binds briefly to receptors on the receiving cell before being cleared — either by reuptake transporters that pull it back into the releasing neuron for reuse, or by enzymes that break it down in place.

The strength of the signal depends on how much is released, how long it remains in the synapse, how sensitive the receptors are, and whether any inhibitory feedback is active. Psychoactive substances disrupt one or more of these steps.

Relevance to substances & effects

Most psychoactive substances work by interfering with neurotransmitter systems. They do so through a few recurring mechanisms: acting as agonists (mimicking the neurotransmitter at its receptor), antagonists (blocking the receptor without activating it), reuptake inhibitors (slowing clearance so the signal persists), or release agents (driving a surge of neurotransmitter into the synapse).

Stimulants such as amphetamines drive dopamine and norepinephrine release and block their reuptake. Opioids bind directly to opioid receptors that the brain's own endorphins normally occupy. Classic psychedelics activate serotonin's 5-HT₂A receptor. Cannabis cannabinoids engage the endocannabinoid system. Benzodiazepines and alcohol enhance GABA, the nervous system's main inhibitory neurotransmitter, producing sedation and reduced anxiety.

Knowing which neurotransmitter a substance targets — and how — frames its expected effects, its interactions with other drugs, and its potential for tolerance or dependence. The pharmacological descriptions across this encyclopedia tie each substance back to this layer.