"Unlike alcohol or tobacco, heroin causes no ongoing toxicity to the tissues or organs of the body. Apart from causing some constipation, it appears to have no side effects in most who take it. When administered safely, its use may be consistent with a long and productive life. The principal harm comes from the risk of overdose, problems with injecting, drug impurities and adverse legal or financial consequences."
Byrne, Andrew, MD, "Addict in the Family: How to Cope with the Long Haul" (Redfern, NSW, Australia: Tosca Press, 1996), pp. 33-34, available on the web at http://www.addictinthefamily.org/.