What describes a drug that affects mood and behavior sold illegally?

The term that best describes a drug affecting mood and behavior and is often sold illegally is narcotics. Narcotics are substances that can induce a state of euphoria and can alter an individual's mood or emotional state. They often have sedative effects and can create a sense of well-being but also come with the risk of addiction and various side effects. Narcotics encompass a range of substances, including both legal prescription medications when misused and illegal drugs, which are often trafficked due to their psychoactive properties.

While analgesics are pain-relieving medications and can also influence mood (such as opioids), they are primarily classified based on their pain-relieving effects rather than their illegal status. Stimulants are drugs that increase alertness and energy and can also influence mood but do not primarily alter behavioral aspects in the same way that narcotics might. Hallucinogens, on the other hand, are known for altering perception, mood, and thought processes but are specifically defined by their capacity to cause hallucinations rather than the broader category of mood and behavior modification that narcotics provide. Thus, narcotics are the most fitting term for describing drugs that impact mood and behavior while being sold illegally.