So almost every time my boyfriend does opiates he gets an erection or chubs. He doesn't necessarily just get horny and then gets an erection, it just sort of "pops up". Some opiates sometimes cause him to get a full erection (heroin, hydromorphone, oxy) and others tend to just give him chubs (semi erections). But it takes wayyyy longer for him to cum if we do end up having sex on opiates. My question is why do opiates give him erections? I tried looking it up and though I found out that it happens to a lot of other guys, I couldn't find an answer for why it happens.