You should never take medication if it hasn't been prescribed to you, no matter what it is. You also don't know what's preventing you from keeping an erection. It might not be caused by something physical at all. Erectile dysfunction (when a man cannot get or maintain an erection) has a number of different causes.

With someone as young as you are, you should get checked by your doctor or clinician to see whether anything physical is going on. Remember that our brain is the most powerful sex organ we have—so something as minor as stress can affect your ability to get and keep an erection. So if it keeps happening, get it checked out!

Again, Viagra is a medication that is prescribed to people with certain medical conditions. It should not be used recreationally. Some teenage and adult males who have abused Viagra have ended up in the emergency room. It’s just not worth it.