It's important to notice the signs related to a substance abuse problem in teenagers.' If you see their grades dropping, that's a big sign. If you notice that they are suddenly wearing perfume more than usual to cover up the smell. If they have changed their friends recently. If they are dressing differently. These are things you would notice all of a sudden. If they seem more tired than usual. If they seem more energetic or talkative than usual. If you notice any major changes in the way they are acting. Obviously, if you see red eyes or visine around, this could be a sign that they are using. These are some of the signs that a teenager is using drugs or alcohol.