As we have seen in previous weeks, the human brain is an extraordinarily complex and fine-tuned communications network containing billions of specialized cells (neurons) that give origin to our thoughts, emotions, perceptions and drives. Often, a drug is taken the first time by choice to feel pleasure or to relieve depression or stress. But this notion of choice is short-lived. Repeated drug use disrupts well-balanced systems in the human brain in ways that persist, eventually replacing a person's normal needs and desires with a one-track mission to seek and use drugs. At this point, normal desires and motives will have a hard time competing with the desire to take a drug.

discuss how these drugs influence normal synaptic transmission. Compare the actions of cocaine, alcohol, and opiates. How are they alike? How do they differ?