I'd say: DO NOT USE ANY ERECTION MED UNLESS YOU SUFFER FROM ED OR HAVE OTHERWISE BEEN PRESCRIBED BY AN MD. ( MEDICAL DOCTOR ).
Used by healthy people it will "change" the neuropathways which carry the arousal message to the brain. If used when NOT needed you will not only develop a "tolerance" to it ( meaning, less and less effective with each use and higher and higher dose needed for it to work from then on ) but you will also develop side effects, a very usual one is ED as a result of usage without needing to. Others carry even more risk, like possible blindness and heart problems. Especially when pre-existing heart conditions are already in place, some of which you might have and not be aware like arritHydromaxia for instance.
Noone needs these meds for Penis Enlargement, this is NATURAL Penis EnlargementNILE ENHANCEMENT not chemical Penis Enlargement.
Also, if one day you DO develop ED for whatever reason, you might find yourself in a dead-end, having used it and NOT needing it it may then fail to have the desired effect even at much higher dosages.
Read a lot about this stuff, it carries significant risk to it just like any other drug.
Watch adult entertainment, stimulate yourself, if even this way you fail to get an erection...then you DO need viagra, otherwise, stay the hell away.
DLD has brought up a huge point to consider also, you get addicted to getting a hard-on through meds and then you find yourself "needing" to use just to get a bonner. Psichological addiction is the result of it, it is when you CANNOT get hard no matter how hard you try or want. THEN only the pills will help, or so your brain will tell you.
Confusing?! Ask me more and i'll simplify,
Peace,
Mike