Have you ever wondered why opiates like heroin are so addictive?  What is it that makes them so desirable that someone would throw everything else in life away to get them?  Any drug can become addictive, but for some drugs, like opiates, the addiction is not only mental, but deeply physical.

The body has natural neurotransmitters called endorphins which help to regulate the pain from every day wear and tear on the body.  Opiates such as heroin have a similar chemical makeup to endorphins, which is why they work so well to reduce pain, and are exactly the kind of medicine you’d like to have on a battlefield.  Physical addiction arises when someone uses opiates so much that the body reduces the production of it’s endogenous endorphins, so without adding an opiate regularly, the body has no capacity to inhibit the sensation of pain.

For a better picture of how this works check out this documentary:

Opiates and Tranquilizers