Please expect up to 4 to 6 weeks for reimbursement. Take sildenafil exactly as directed. You should not purchase sildenafil without a prescription, as the medication could cause serious harm. Ask your healthcare professional how you should dispose of any medicine you do not use. Maintaining optimal testosterone levels can greatly impact overall health, fitness, and Does Creatine Increase Testosterone: Uncovering the Truth Does Creatine increase testosterone levels? Do not take more or less of it or take it more often than prescribed by your doctor. It works for up to 36 hours.You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription. Travel. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction (ED). Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Drug Facts Common Brands Viagra Drug Class PDE-5 inhibitor Controlled Substance Classification Not a controlled medication Generic Status Lower-cost generic available Availability Prescription only How Sildenafil (Viagra) works Sildenafil (Viagra) is a phosphodiesterase-5 (PDE-5) inhibitor.