Do not keep outdated medicine or medicine no longer needed. If too much is used, the chance of side effects is increased. Some of these drugs can interact with prescription drugs and cause dangerously low blood pressure. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. What side effects can this medication cause?VIAGRA is available by prescription only in 25 mg, 50 mg, and mg tablets. Patients should always ask their doctors for medical advice about adverse events. You are . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in . · Proper Use. Drug information provided by: Merative, Micromedex ®. Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it .