Summarize this article:

Cocaine and other stimulants often cause overly-energetic behavior. Common conversational clues of cocaine use include:  excessive talkativeness  rapid speech  conversations that jump around from one topic to another Cocaine use frequently gives users a sense of invincibility. This can lead to high-risk behavior, including risky sexual activities, and violent tendencies, such as fighting, domestic violence, homicide, and suicide.  Risky sexual activities may lead to pregnancy, illness, and/or sexually transmitted infections.  High-risk behavior may lead to legal problems, serious injury, or death. Someone who consistently uses cocaine may end up spending large amounts of time and energy acquiring cocaine. Users of cocaine may also engage in:  shirking responsibilities or obligations  frequently disappearing, going to the bathroom, or leaving the room, and returning in a different mood Because cocaine is a stimulant, it can cause sudden changes in mood. This may mean irritability, but it could also cause sudden bursts of euphoria or a sense of carelessness, or a shift from one extreme to the other. A common behavioral characteristic of people who use drugs is withdrawing from social relationships, either to be alone or to be with others who use drugs. Though socially withdrawing from a group of friends may be caused by other factors, such as anxiety or depression, it may also be a sign of drug use. Many users of all kinds of drugs experience a loss of pleasure in activities or interests that had previously been enjoyable, but this is particularly problematic with cocaine use. That's because cocaine use harms the circuits in the human brain that are responsible for a sense of pleasure. Look for signs of depression and a seeming lack of pleasure in day-to-day activities as a symptom of long-term cocaine use.

Summary:
Spot conversational clues. Look for risk-taking behavior. Notice other behavioral changes. Look for dramatic mood swings. Notice social withdrawal. Note a loss of pleasure.