Many aspects of the human body are controlled by the Endocrine system.
Simply put, the endocrine system is a network of glands that secrete chemicals called hormones to help your body function properly. Hormones are chemical signals that coordinate a range of bodily functions – including sex.
It is important to note the amount of these chemicals actually produced is a very small volume, seldom more than a drop or two. Is it any wonder that even small amount of Drugs & Alcohol can impact this chemical balance.
These links provide overviews on some important aspects of the male body. Especially if you like chocolate.