Traumatic brain injury and methamphetamine: A double-hit neurological insult

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality in the world. TBI causes permanent physical, cognitive, social, and functional impairments. Substance use and intoxication are established risk factors for TBI. Data are emerging that also suggest that brain injury might be a risk factor for substance use. Methamphetamine (METH), a highly addictive psychostimulant, has not been thoroughly investigated in the context of TBI exposure. The interplay between the two has been of interest as their pathophysiology intertwines on many levels. However, the knowledge concerning the association between TBI-METH and the impact of chronic METH use on short and long-term TBI outcomes is equivocal at best. In this review of the literature, we postulate that, when combined, these two conditions synergize to result in more significant neuronal damage. As such, chronic exposure to METH before brain trauma may accentuate the pathophysiological signs of injury, worsening TBI outcomes. Similarly, individuals with a history of TBI would be more vulnerable to METH misuse and harmful effects. We, therefore, review the most recent preclinical and clinical data tackling the significant overlap in the pathophysiology of TBI and METH at three levels: the structural level, the biochemical level, and the cellular level. We also highlight some controversial results of studies investigating the outcomes of the interaction between TBI and METH.