Sign: Anxiety
"I've always considered myself a bit of worry wort, but it's nothing like how much my daughter worries. She literally shakes when she goes into a store with me, as if she is afraid of being there. She constantly talks on and on about how she is going to fail tests. She is a smart girl and used to be very confident. Now she seems like ball of nervous energy."
First you will need to rule out any endogenous cause for this anxiety - a clinical professional or physician can examine your teen to make sure their isn't an underlying cause. If your child is developing social phobias, it is important to seek professional help.
Some drugs can make teens more anxious - even withdrawal can make them seem more jumpy or even paranoid. Sometimes drugs make teens withdraw from the world around them. When they are forced into public situations, they may feel uncomfortable, anxious, and even paranoid. Remember to look at the signs of drug use as a group of signs - one isolated sign is not necessarily indicative of a problem.