The dosage of Vidalista 40 is one of the most well-known drugs used worldwide to treat erectile dysfunction, or ED, or impotence. Tadalafil is the active ingredient in Vidalista. By relaxing the blood vessels and penile muscles, it improves blood flow and makes erections easier for men. Take Vidalista a few minutes after having sex to help with erection. Be aware that common side effects include flushing and temporary vision changes.