What factors are considered in the assessment of damages for a plaintiff's drug use prior to her accident?

The first is the evidence of the plaintiff's pre-accident drug use, including cocaine addiction. This is an important factor, because the assessment of tort damages requires comparison of a plaintiff's with-accident condition to the condition they would have attained had the accident never occurred – a plaintiff's “original position”. To ensure that a defendant justly and appropriately compensates a personal injury plaintiff, through an award of damages that restores the injured plaintiff – as much as can be done through a monetary award – to the state they would have been in had the injury never occurred, consideration of the “original position” entails not only examination of the plaintiff's condition immediately prior to the time the subject injury was sustained, but also consideration of what condition the plaintiff would have gone on to attain but for the defendant's negligent conduct. A defendant is fully liable for all loss and damage caused by their tortious conduct, but “need not put the plaintiff in a better position than his original position and should not compensate the plaintiff for any damages he would have suffered anyway” (per McLachlin C.J.C. in Blackwater v. Plint, 2005 SCC 58, at para. 78, referring to Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458).