Heroin, being an opiate, is a depressant drug. It produces initial stimulation of the central nervous system, followed by a more marked depressant effect. Effects last 4-6 hours. Heroin causes depression of the gastro-intestinal system, and constipation can occur. High doses can cause vomiting and drowsiness.
Excessive dose can cause unconsciousness and death.
Although legally defined as a narcotic, cocaine is a stimulant drug. It stimulates the brain cortex, and central nervous system. Overdoses produce anxiety, depression, headache, confusion and fainting, and occasionally convulsions and respiratory failure. It appears some people are hyper-sensitive to cocaine, and in them small doses can produce dangerous toxic reactions. Overdoses occur more often when the cocaine is prepared as crack for smoking.