My teenage son seemed to have "recovered" from a rapid plunge two years ago into serious drug abuse (ketamine, MDMA, ecstasy), ending last year. Since then he seemed to be "just" making steady use of pot. Recently however he has been coming home once in a while with dark circles around very sunken eyes, and a ghostly white complexion. There is no major personality shift on those occasions, except that he's quieter than usual, and will sometimes go to bed unusually early. Does this point to the use of a particular drug?