You can take Viagra (sildenafil) if you have high blood pressure that is controlled by blood pressure medications. Viagra (sildenafil) works by blocking an enzyme called PDE-5, which, in turn, prevents the break down of another substance called cGMP, which causes smooth muscle to relax and dilate. This allows more blood to flow to the penis and also causes blood vessels around the heart to open wider. This effect is called vasodilation, and it lowers blood pressure.

Viagra is used to treat erectile dysfunction in men. You should tell your doctor if you have high or low blood pressure before starting Viagra.

Caution is warranted in some cases:

• If you take Viagra with a blood pressure medication that also works by lowering blood pressure through vasodilation, your blood pressure could drop low enough to make you dizzy or make you pass out
• Taking Viagra with a blood pressure or prostate medication called an alpha blocker can be dangerous. If you take an alpha blocker and you need Viagra, your doctor may need to lower the dose of the alpha blocker or lower the dose of Viagra
• Another type of drug that lowers blood pressure is a nitrate drug. Nitrate drugs are used in people with heart disease to relieve chest pain called angina. You should not use Viagra if you use a nitrate drug. This can also lead to a dangerous drop in blood pressure.

Blood pressure is measured in units called millimeters of mercury (mmHg). The higher number in a blood pressure measurement is the pressure in your arteries when your heart pumps, called the systolic pressure. The lower number is the pressure between heartbeats, called the diastolic pressure. Studies in healthy volunteers show that a single dose of Viagra lowers systolic blood pressure by about 8 mmHg and diastolic pressure by about 5 mmHg.

You should tell your doctor if you have high or low blood pressure before starting Viagra. You should also tell your doctor about all the medications or supplements you take. If you take a medication or supplement that lowers blood pressure along with Viagra, it may drop your blood pressure too much, which could make you dizzy or fall over. This is called hypotension.