Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Take sildenafil at around the same times every day. If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. This site is intended only for U. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. · Is Viagra prescribed in dosages of mg, mg, or mg? The highest recommended Viagra dose for treating erectile dysfunction (ED) is mg per day, according to the drug’s manufacturer. Viagra dosage for erectile dysfunction (ED) is usually milligrams (mg), but those over 65 may start at 25 mg. Your doctor will also need to consider possible drug interactions. Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. VIAGRA may affect the way other medicines work, and other medicines may affect the way VIAGRA works, causing side effects. Especially tell your healthcare provider if you take any of the following.