You should only be treated with one of these products at a time. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. This medicine works best when you take it on an empty stomach an hour before sex. 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. The body takes longer to absorb it after a high-fat meal or alcohol.Viagra vs. over-the-counter products. Many over-the-counter (OTC) products may be advertised to help with ED. Examples of these products include: . 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 . In fact, a recent review of studies found that some counterfeit drugs contained a very high, dangerous level of sildenafil that far exceeded a typical .