A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil. Sildenafil may cause side effects. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Common ones include: Flushing of the skin.You should not take Viagra more than once daily. And you should only take it as needed. Long-term use. No, you should not take Viagra if you don’t have ED. Viagra is a prescription medication that can have serious side effects. And it’s approved only to treat ED, not to be used . What to consider Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a .