First time use of heroin can cause nausea, vomiting and severe headaches. Generally, however, the drug creates a high a few minutes after it has been smoked or injected. Injection leads to a quicker, more powerful high, but sharing needles can increase the risk of infection. Users often experience a feeling of well-being, contentment and detachment from daily worries.

Tolerance builds up with use so greater amounts of the drug are needed to create the high. This can eventually lead to addiction. It also increases the risk of overdosing. Research shows that overdose often occurs after users have tried to come off the drug. When they start taking it again, they often resort to the dose they were on when they stopped, although their tolerance is not as high.

The fact that heroin is often adulterated with other substances can also cause overdose. Symptoms of an overdose include rapid heartbeat, heart failure, shortness of breath, unconsciousness and coma. When unconscious, the user is at risk of choking on their own vomit.

Heroin can also cause unexplained sudden death due to the user having a particular reaction to the drug, to injecting heroin and to impurities present in the drug. Long-term effects of injecting heroin include collapsed veins, loss of appetite and severe constipation. Heroin use is also associated with crime as the drug is expensive to obtain. Pregnant women who use heroin risk giving birth to small babies who may be addicted to heroin and suffer withdrawal symptoms. Withdrawal usually lasts several weeks and symptoms include aches, tremors, sweating and spasms. These usually fade after a week, but it may take months to regain a sense of natural well-being.