■ The drug, which is not found in nature, was created by scientists looking for a nonaddictive substitute for morphine.

The result — heroin — is a drug with four times the pain relieving effect and several times the addictive potential.

■ Withdrawal can begin within a few hours after last use in regular abusers. Withdrawal symptoms include drug craving, restlessness, muscle and bone pain, insomnia, diarrhea and vomiting, cold flashes with goose bumps, kicking movements and other symptoms.

■ Major withdrawal symptoms peak between 48 and 72 hours after the last dose and subside after about a week.

■ Sudden withdrawal by heavily dependent users who are in poor health is occasionally fatal.