hi; Psoriasis is an auto-immune skin disorder it come on due to some trigger like stress mental/physical ;odd working conditions & as sudden impact of some bad news like death of a close one;or accident & occassionally aggravated because of some allergic thing .Psoriatic arthritis is a complication of it.Now the big question is whether you had psoriasis before abuse of Methamphetamine .If yes then you see the reason is not abuse ;& if you did not have before then it can be because of abuse.In any case even if Methamphetamine abuse is not the cause of Psoriasis ;it will always act as the aggravating factor so please discontinue abuse of the said drug. thanks