In many of the studies, of both fixed dose and titration designs, daily diaries were kept by patients. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. As in the other titration studies, patients were started on 50 mg and allowed to adjust the dose up to mg or down to 25 mg of VIAGRA; all patients, however, were receiving 50 mg or mg at the end of the study. Protein binding is independent of total drug concentrations. During 3 to 6 months of double-blind treatment or longer-term 1 year , open-label studies, few patients withdrew from active treatment for any reason, including lack of effectiveness. The FDA recommends avoiding alcohol use if you take this drug.Por otro lado, segun el NHS, la Viagra puede causar efectos secundarios graves en menos de 1 de cada pacientes. Se recomienda dejar de tomar las pastillas y consultar con un medico: si. Vision changes. Muscle pain. But there are some differences. With Viagra, there is a higher risk of vision changes than with Cialis. Among people who take Viagra or sildenafil, 3% get blue vision that lasts a few hours. On the other hand, Cialis has a slightly higher risk of muscle pain than Viagra and vardenafil. Viagra is absorbed quickly into your body. It can start working within 30 minutes, but it may take a couple hours for some people. However, one study on Viagra found that about 70% of men achieved erections in 30 minutes, and more than 80% of men achieved erections within 45 minutes. For most men, the effects of Viagra will start within .