Heroin produces a ‘rush’ minutes after taking it, leading to a feeling of warmth and contentment. In larger doses it can cause the user to feel drowsy and very relaxed. Heroin is also known to greatly reduce physical and psychological pain when taken. A central nervous system depressant, heroin actually slows down the brain functions, and in particular the control of breathing, which can slow down or even stop. At the same time blood pressure and body temperature drops and the heartbeat can become irregular.