Sildenafil and Tadalafil are medications used to treat erectile dysfunction (ED) in men. Both work by relaxing blood vessels and increasing blood flow to the penis, helping achieve and maintain an erection during sexual activity. Sildenafil (commonly known as Viagra) usually takes effect within 30-60 minutes and lasts for about 4-5 hours. Tadalafil (known as Cialis) takes effect within 30 minutes and can last up to 36 hours, offering a longer window of opportunity. Both drugs require sexual stimulation to be effective. Side effects can include headaches, flushing, and indigestion. It's important to follow your doctor’s guidance when using these medications, and they should not be taken more than once a day.