For English Instructors - Writing a Thesis Statement ?

Alright, so I am by no means an English Instructor but I thought it couldn't hurt to give my two cents worth (perhaps literally? lol). In the introductory paragraph perhaps you could mention something about the negative affects drugs have on one's life (or some other broad statement) and then continue to narrow into drug addiction and it's causes. From what you have written it seems as though you are trying to discuss with and inform the reader of the causes of drug addiction, not the effects of the substance(s). Perhaps you could talk about the emotional and/or psychological triggers (ie child abuse, growing up in a tumultous household, peer pressure, boredom) in the first paragraph, the neurological triggers the substance(s) cause(s) (ie marijuana affects neurotransmitters, alters brain function and memory) in the second paragraph, and in the third you could discuss the physiological dependence of the body on a substance. I hope this helped - good luck!