Diuretics and Hypotensive Agents: When minoxidil is administered with diuretics or other hypotensive drugs, the hypotensive effect of minoxidil is increased. The effect is usually used to therapeutic advantage, but careful adjustment of dosage is necessary when these drugs are used concomitantly. Minoxidil should be administered with caution to patients receiving guanethidine, since concurrent use may cause profound orthostatic hypotensive effects. If possible, guanethidine should be withdrawn several days (1-3 weeks) before minoxidil therapy is begun. If minoxidil must be started in patients receiving guanethidine, the patient should be hospitalized until severe orthostatic effects subside or the patient has learned to avoid activities that cause postural hypotension.