Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Do not mix the liquid with other medications or add anything to flavor the medication. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Its effects might last longer if you have mild to moderate ED. Take sildenafil exactly as directed. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take.What to consider Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a . No, you should not take Viagra if you don’t have ED. Viagra is a prescription medication that can have serious side effects. And it’s approved only to treat ED, not to be used . Viagra or generic sildenafil for ED should not be used in women. For seniors: The kidneys, liver, or heart of older adults may not work as well as they used to. This can cause your .