Sexual activity may be a strain on your heart, especially if you have heart disease. If you prefer, you may contact the U. This increased blood flow can cause an erection. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Sildenafil usually should not be taken more than once every 24 hours. How should this medicine be used?What Happened When I Took Viagra Recreationally. 1. Viagra was effective for much longer than four hours. Shutterstock. Viagra comes in three different sizes: 25mg, 50mg, or mg. In the past, I’ve found that 25mg always did the job just fine. However, my journey begins with a bottle of the mg tabs which I’ve chosen to cut into thirds. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . Hims is a telehealth company that provides both prescription and over-the-counter generic and brand-name medications. The brand focuses mainly on five medications, including Viagra, that have.