How can heroin affect the central nervous system?

Depressant effects: After the initial effects, heroin abusers may be drowsy for several hours. Mental function is also clouded by heroin's effects. Cardiac function slows, as does breathing, sometimes to the point of death. Heroin overdose is extremely dangerous due to these depressant effects on the cns.

Very complex: Heroin (diacetylmorphine) is converted to morphine in the brain & attaches to mu opioid receptors. In the medulla it depresses breathing. In ventral tegmental area (vta) it reduces gaba. By inhibiting this inhibitor, opiates increase the amount of da released (the reward neurotransmitter) by the vta into the nucleus accumbens of the basal ganglia, which is a major pleasure center of the brain.