"They warn you against taking nitrates, but I guess cannabis should be fine right?"
Marijuana and viagra are both metabolized by cytochrome CYP3A4, but neither medication is considered either an inhibitor or inducer of the enzyme; so, drug metabolism should not be affected. Viagra is a phosphodiesterase inhibitor which results in vasodilation. Cannabis has mild vasodilation effects, so theoretically could enhance the effects of viagra; although to my knowledge, this has not been investigated.
Dr Edmunds
According to the Mayo Clinic ""may cause increased effects or potentially serious adverse reactions".
Sally B
