PRL and familial hyperprolactinemia: The mechanisms by which drugs lead to HPRL are: inhibition of dopamine by antagonistic action of these substances on dopamine receptors (antipsychotics and metoclopramide) or inhibition of dopamine synthesis (estrogen).(32) Other substances can act on the secretion of factors that alter the tonic suppression of PRL synthesis such as serotonin and GABA.