Hey, you inject talc into your skin, that's what you get. The life-style that an addict leads is generally pretty unhealthy as well. Often, addicts don't get an adequate diet. Vitamin deficiencies are not uncommon. Constipation caused by a combination of poor eating that the effects of the drug on the bowels can lead to haemorrhoids.
Chest infections seem pretty common too, especially among cigarette smokers.
So, it would seem that if one had clean heroin from a reliable source and avoided the IV route, there'd be few health problems. Potential problems would arise from becoming addicted and becoming unproductive or from accidentally ODing. In the lab, it takes a couple weeks of 3 shots a day before one gets withdrawl symptoms. So, if you avoid hanging around hardcore addicts, it is not that hard to avoid an addiction. The existence of non-addict users shouldn't be surprising.