Like all benzodiazepines, lorazepam works primarily on the gamma-aminobutyric acid (GABA) receptors in the brain, which control the absorption of GABA, the main inhibitory neurotransmitter. Its actions are similar to those of diazepam (valium) but it is considerably more potent, and therefore only requires much smaller doses (hence the 1mg and 2mg tablets, as compared to 2, 5 and 10mg for diazepam).
The absorption time depends on the method of intake; orally, peak plasma concentrations are about 2 hours after ingestion. Intravenously, the absorption is quicker, generally around the hour mark.
Lorazepam’s half-life (the time it is effective in the body) is an average of 12 hours for a standard dose. It has a very high rate of bio-availability (up to 90%) and is rapidly conjugated at its 3-hydroxy group into lorazepam glucuronide. This is then excreted in urine.