- Currently receiving guanethidine, pressor agents, MAO inhibitors, coumarin anticoagulants, anticonvulsants (e.g. phenobarbital, phenytoin, primidone), phenylbutazone, tricyclic antidepressants (e.g. imipramine, desipramine), selective serotonin reuptake inhibitors (SSRIs) or herbal remedies (unless on a stable dose for 4 weeks).