Why can t I build a tolerance to opiates?

Okay, let me preface by saying I KNOW I HAVE A SUBSTANCE ABUSE PROBLEM. I have been to rehab and I am slowly but surely recovering and weaning myself off. This is more curiousity than asking how I can continue using without side effects. I ve been using heroin and roxycodone for about a year now, usually a gram or 4 pills a day. Despite a very regular habit, I am constantly vomiting because of this habit. Why have I not built a tolerance yet? Is it possible I am allergic to these substances? Again, purely curious, and genuinely perplexed.
Answers

USAFisnumber1

You are confusing a tolerance to a drug with a tolerance to the side effects of a drug. You are one of those people who get sick from narcotics and no matter how long you take it or how much or how little, you will still get sick from it.

Anonymous

Genetics. It is not uncommon for our body to reject harmful substances. In fact, drug addictions as well as smoking addiction and other types of addictions are a metabolic condition according to pharmacologists. That's a positive thing that your body is defending you from harm.