The two key telltale signs of addiction or drug abuse are physical and emotional. So physically, you'd notice that there are profound changes in the person. Changes in the way that they dress. Changes in the way that they take care of themselves. Physical changes, there could be changes in their body weight. They could either be gaining a lot of weight or losing a lot of weight. Emotionally, you want to look at their behavior.
You want to look at mood swings. Are they experiencing really high high's and really low low's? Also, you want to look at irritability. Is the person really irritable? Are they defensive? Are they, if you bring up the topic of drug addiction or drug use, do they get incredibly defensive about it. So those two things are the key factors that you should be looking for. These physical changes and these emotional reactions and these emotional changes in the person.