If approved, the provider will issue a prescription. These PDE5 inhibitors may cause headache, flushing, drop in blood pressure, or other adverse effects. However, others work on a cash-pay basis and don’t partner with insurance companies. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food. Make sure to get an estimate of when you can expect your prescription in the mail.About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when. 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.  · For example, a year-old might start at a dose of 50 milligrams (mg), while a year-old might have a starting dose of 25 mg. This is because, in older people, the body clears Viagra from your.