Recent heart or blood vessel problems. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. There were some reports of headaches and nausea, however. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Vardenafil usually works for 4 to 5 hours.Treatments for erectile dysfunction are big business, and online scams abound. If you do buy medicines over the internet: Check to see if an online pharmacy .  · a light-headed feeling, like you might pass out. Common sildenafil side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; . 3. You Should Still See Your Doctor. The OTC gel for ED will help you get relief quickly. But, keep in mind that ED might signal an underlying medical problem, like Missing: walgreens.