The benzodiazepine family of tranquillizers, which includes diazepam, has anxiolytic, sedative, muscle-relaxant, amnestic, and anticonvulsant properties. The production of active metabolites, primarily desmethyldiazepam, improves its action. The increase of GABAergic neurotransmission at inhibitory synapses is the mechanism through which benzodiazepines exert their central effects. Positive allosteric regulation of the GABA receptor’s affinity for the neurotransmitter occurs in the presence of benzodiazepines, increasing the effect of released GABA on postsynaptic transmembrane chloride ion flux.

When taken orally, diazepam is quickly and completely absorbed from the gastrointestinal tract, peaking 30-90 minutes after consumption.

Desmethyl-diazepam levels take roughly twice as long as diazepam to achieve a steady state after daily dose; they do so in around 5 days. After a once-daily dose, mean steady-state levels of diazepam are around twice as high as their peak levels.

Due to a decrease in hepatic clearance during treatment, the elimination half-life of diazepam may be increased by 50%. There are conflicting reports on how plasma levels change throughout the course of long-term therapy. Diazepam levels have been reported to significantly drop throughout the course of long-term therapy, probably as a result of metabolic autoinduction. However, in other studies, plasma concentrations of diazepam and its desmethyl metabolite were unaffected by the length of therapy.