Assertion: viagra's effect | /r/HasProperty | natural chemical
Facets:
Source sentences:
text: Sildenafil (Viagra), vardenafil (Levitra, Staxyn), tadalafil (Cialis) and avanafil (Stendra) are oral medications that reverse erectile dysfunction by enhancing the effects of nitric oxide, a natural chemical your body produces that relaxes muscles in the penis.
text: All four medications enhance the effects of nitric oxide — a natural chemical your body produces that relaxes muscles in the penis.