Can heroin cause hyperglycemia?

I am not sure. Representatives from the U.S. National institutes of health (nih), the american diabetes association (ada), and the juvenile diabetes research foundation (jdrf) report that they are unaware of any such studies on the topic of illicit drug use and blood glucose control.
Not usually. Heroin is rarely associated with low blood sugars, not high. It is frequently cut with a variety of sugars, and the cutting agent (mannitol, inositol) can be responsible for raising blood sugar transiently, but a normal pancreas will then produce enough Insulin to get the blood sugar to normal quickly. I am concerned about your question. Heroin is a dangerous and nasty drug. Get help if using.