While no intravenous drug is 'harmless', there is some truth to this adage. Unlike alcohol or tobacco, heroin causes no on- going 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.
Injected heroin can never be 'safe' when the exact dose is unknown.
Apart from sedation, rare but well documented side effects of narcotics include dry mouth, sexual abnormalities, growth of breast tissue in males, menstrual irregularities in women and excessive sweating. These can occur with all opioids such as codeine, morphine, heroin and methadone. The symptoms are usually mild and self-limited, but occasionally they may be trigger factors inducing addicts to curtail their drug intake.