If a man is on high blood pressure medicine, can he still safely take viagra (sildenafil)?

Yes, unless nitrate: Viagra and its competitors can be taken in conjunction w/most other medications except nitrates. The combination of viagra & nitrate can lead to abrupt excessively low blood pressure, enough to kill someone, so don't do it! and be careful of otc dietary supplements that purport to be all-natural pure organic alternatives to viagra. Often they only work because they are contaminated w/sildenafil.