With this pattern of abuse, tolerance develops to many of the effects of heroin, but it develops at different rates for different effects. Pain suppression tends to be the first effect which users build up tolerance to. Constipation and small pupils are the last. Although the feelings of euphoria lessen, the drug provides enough pleasure to be reinforcing. The signs of withdrawal include, watery eyes, runny nose, yawning and sweating.
Heavy users experience mild withdrawal as soon as the most recent dose wears off.
As withdrawal continues the user feels restless and irritable and loses his appetite. Symptoms are similar to that of the flu. At peak the symptoms include diarrhea, shivering, sweating, general malaise, abdominal cramps, muscle pains as well as difficulty sleeping. The craving for heroin will last for months, long after the physical symptoms of withdrawal have ceased. There are so many factors that affect the action of the drugs, that it is impossible to accurately consider them all.