Some opioid agonist-antagonists, partial agonists, and inverse agonists are also derived from morphine. Medications used include stimulants, atomoxetine, alpha-2 adrenergic receptor agonists, and sometimes antidepressants. They include GnRH agonists and GnRH antagonists. Hormones are also regulated by receptor agonists. Many ACh receptor agonists work indirectly by inhibiting the enzyme acetylcholinesterase. Several D receptor agonists are used clinically. Dopaminergic drugs such as reuptake inhibitors and dopamine agonists may also increase risk of switch. Such medications include antipsychotics, antidepressants, anticonvulsants, alpha agonists and anticholinergics. Antagonists reduce or block the signals of agonists. Efficacy increasing modulators increase maximum efficacy of partial agonists. Azapirones are a class of 5-HT receptor agonists. Once bound, however, antagonists inhibit the function of agonists, inverse agonists, and partial agonists. For opioid agonists and opium derivatives, these are classified differently. Cessation of dopamine agonists therapy may also be of use. Combination treatment with dopaminergic agonists such as cabergoline is also possible.