Dopamine depletion hypothesis of cocaine dependence: A test

Measurements of plasma homovanillic acid (HVA), plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), serum prolactin and Hamilton Depression Rating Scale (HDRS) scores were made in 21 cocaine-dependent patients seeking inpatient treatment. These measurements were obtained within 1–3 days of the last dose of cocaine and were repeated after 10–20 days of abstinence from cocaine. Abnormal values on any of the biochemical measurements were unusual and showed no convincing evidence of dopamine or norepinephrine depletion. Ten patients had significant HDRS scores on admission which decreased by 50% or more during hospitalization without specific treatment. The controversy over whether chronic exposure to cocaine depletes dopamine remains unsettled. Howevr, it is more likely that down-regulation of postsynaptic dopamine receptors is the major consequence of such exposure.