Question: How do drugs such as Viagra affect blood pressure?
Answer: A drug such as Viagra, which is a drug that enhances nitric oxide, and nitric oxide is a vasodilator -- and that means that it can lower blood pressure. So Viagra can contribute to a lowering of the blood pressure, especially if one is on other blood pressure-lowering drugs or drugs like nitrates -- nitroglycerine, isosorbide -- drugs that normally work in a similar way as Viagra.
But I would think that other blood pressure drugs and Viagra may act in a synergistic or additive way to affect the blood pressure. So I would be sure that your doctor knows what other drugs you're on before you take Viagra.