This is a great question and a tough one to answer at that. Many in the medical field claim testosterone is the main hormone responsible for libido. I also know that on average, men’s testosterone levels increase by about 10% when on finasteride because less of it is being 5 alpha reduced to dht. But that begs the question...why do people get side effects?
i have a feeling it has to do with the body failing to meet equilibrium with all hormones after dht is lowered dramatically. This is just my thought though.