Why do you develop a tolerance to opiates?

Scientifically speaking?

opiates mess with the chemisty of the brain. causing a good feeling. It doesn't really make you stop feeling pain just cause's you to not care. same as marijuana, and nitrisoxide. Just as with antibiotics. your body builds defense's that cause them to not work as well. there for you need more and more to make them work the same as they did when you started taking them.

Opiates are pain killers. Our body naturally contains pain killers but opiates are a synthetic form of what the body already has. When someone begins taking large quanities of pain killers the body shuts down producing its natural defenses. That is how the tolerence occurs. The body no longer produces the substance so more pain killers are needed to produce the high or supress pain.