How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Follow your doctor’s orders or the directions on the label. These medicines are called PDE5 inhibitors. If you see air bubbles in the syringe, repeat the steps. That means seven out of 10 people who take these drugs as prescribed will have more frequent or longer-lasting erections. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse.Drugs including Viagra and Cialis lead to an average improvement of 4 to 8 points on the scale used by researchers and clinicians. The team behind the new study suggests that . Sildenafil (Viagra brand) only works following sexual stimulation. It works within 30 to 60 minutes, but may be taken up to four hours before sexual activity. Sildenafil (Revatio . Viagra doesn’t work on its own. You’ll still need to feel sexually aroused to get an erection. Feeling relaxed and comfortable can also help Viagra take effect sooner. The average .