My daughter's drug of choice is meth...when she was active in her use, she would spend up to two hours in the bathroom picking at her face. But when she was REALLY bad, she started digging at her arms with paperclips....pins... whatever she could find. She said it felt like bugs crawling under her skin.
The long-term meth users in my town are almost always fairly scarred up, their teeth are mostly gone and they tend to look very much alike.
It is not a good thing.