See What Weed Does To Your D**k

In 2010 researchers first discovered THC receptors inside a monkey penis, and then eventually, the human penis. The receptors themselves are located in the smooth muscle of the penis. That noise makes up almost 80% of a dude's johnson and thus, must be taken seriously.
Testing began, and soon there were indications that THC, the active ingredient in marijuana, could be linked with sexual dysfunction with those receptors being to blame.
Long-term pot users have reported a decrease in their sexual function. This is pretty interesting given that most users still report (and have since 1973) that smoking enhances their sex life. But again, these were younger users.
Don't go burning down your secret stash just yet.

There's a pretty major flaw in this study, and it's one researchers are hard at work to solve. Men in general report higher instances of sexual dysfunction as they age. Good ol' mister floppy does love to start messing with a dude's head, don't he?
In order to accurately determine whether age or pot usage is the defining factor, more research needs to be conducted.
If this means some women have to volunteer to get high and have some sex on the government's dime, I am more than happy to offer up my services to the cause. Science is important.
Do you think it's true?