Acamprosate-d is intended for use as an internal standard for the quantification of acamprosate by GC- or LC-MS. Acamprosate is an acetylated derivative of the GABA analog homotaurine (tramiprosate; ). Despite its structural similarity to GABA, acamprosate does not act at GABA receptors but does decrease paired-pulse inhibition of GABA inhibitory post-synaptic currents (IPSCs) at short inter-stimulus intervals when used at a concentration of 300 µM, indicating that it may inhibit GABA autoreceptor-mediated inhibition of GABA release. It is an NMDA receptor modulator with antagonist or agonist effects depending on brain region, receptor subunit composition, and other factors. Acamprosate (0.26 and 0.52 mmol/kg per day, i.p.) reduces voluntary intake of ethanol in rats, an effect that can be blocked by the GABA antagonist bicuculline . Formulations containing acamprosate have been used for the maintenance of alcohol abstinence.