Final answer:
The best predictor of later use of hard drugs such as cocaine or heroin is the early use of substances such as tobacco, alcohol, marijuana, or prescription drug misuse. This is due to the way in which these substances can alter neurotransmitter systems in the brain and reinforce behaviors that may lead to addiction.
Step-by-step explanation:
The use of tobacco, alcohol, marijuana, or prescription drug misuse in one's youth is the best predictor of whether a person will later use hard drugs such as cocaine or heroin. Studies such as by Molina et al. (2003), on children with ADHD, point towards such early substance use as an important predictive factor for later substance use disorder.
Drug addiction refers to the compulsive use of substances, such as psychoactive drugs, despite negative consequences. The use of softer drugs can lead to the use of hard drugs due to changes in the brain's neurotransmitter systems. These changes result in positive reinforcement that may encourage further experimentation with and addiction to more potent substances. Specifically, the use of drugs that affect dopamine neurotransmission, such as nicotine, caffeine, and certain prescription medications, can lead to further substance abuse.
Providing introductory drugs to children and adolescents can, therefore, be a significant risk factor for later development of addiction to more harmful substances like cocaine and heroin. Education on the risks of starting soft drugs and the potential escalation to harder substances is crucial in preventive strategies.