Sildenafil should not be used with any other medicine or device that causes erections. Adverse Effects Warnings and Precautions Sildenafil has systemic vasodilatory effects and, as such, should be prescribed with caution to patients who may be sensitive to such blood pressure changes, such as patients with left ventricular outflow obstruction and impaired autonomic control of blood pressure. Different brands may not work the same way. Trimazosin Other Interactions Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Dosage and strength for erectile dysfunction Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to mg. Take sildenafil up to 4 hours before you want to have sex. Side Effects Along with its needed effects, a medicine may cause some unwanted effects.Sponsored You may be eligible to save up to 50% on your brand-name prescription * * Terms and Conditions Apply Get Savings Card Pharmacy Offers in Your Area Price and Missing: goodrx. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex. For sildenafil to work properly, you’ll need to be sexually excited. Sildenafil citrate is a white to off-white crystalline powder with a solubility of mg/mL in water and a molecular weight of VIAGRA is formulated as blue, film-coated rounded-diamond-shaped tablets equivalent to 25 mg, 50 mg, and mg of sildenafil for oral administration.