The finding:
Neuromodulation (NM) methods, including repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS) and deep brain stimulation (DBS) may be promising treatments for substance use disorders (SUDs). This study synthesized findings from 94 studies involving a total of 4,306 participants, that examined the effects of rTMS, tDCS, and DBS on substance use outcomes (e.g., craving, consumption, and relapse) amongst individuals with SUDs including alcohol, tobacco, cannabis, stimulants, and opioids. By targeting addiction neurocircuitry, rTMS was shown to reduce substance use and craving, as indicated by medium to large effect sizes (Hedge’s g > 0.5) when multiple stimulation sessions were applied, and the left dorsolateral prefrontal cortex (DLPFC) was targeted. tDCS also produced medium effect sizes for substance use and craving, though results were highly variable and less robust than rTMS and required targeting the right DLPFC. DBS studies, though smaller and less controlled, showed promise in reducing misuse of multiple substances. Notably, electroconvulsive therapy (ECT), magnetic seizure therapy (MST), transcranial alternating current stimulation (tACS), and invasive anterior cingulate cortex (ACC) stimulation were excluded from this review as studies examining their effects on SUDs were limited. This comprehensive evaluation highlights NM as a promising avenue for SUD treatment, advocating for further research to elucidate neural mechanisms, optimize treatment protocols, and evaluate long-term outcomes.

Strength and weaknesses:
There is considerable promise for the use of NM therapies in SUDs and this is the first comprehensive systematic review of the addiction neuromodulation literature aggregating a large sample size from 94 studies and include meta-analytic comparisons that evaluated the treatment efficacy of each stimulation technique, with respect to each SUD and the stimulation parameters applied, and to identify their differential effects across substances. The specificity in examining different neuromodulation modalities (rTMS, tDCS, DBS) and their target brain regions enhances the precision of the findings and contributes valuable insights into the most effective treatment protocols. Limitations of this study, as pointed out by the authors, included their preliminary nature, the presence of heterogeneity among the included studies in terms of methodology, participant characteristics, intervention protocols, in the outcomes evaluated (e.g., craving vs. consumption), and in the methods used to measure them (e.g., biochemical verification versus self-report), which can complicate the interpretation of the results. Also, as substance use was the primary outcome of interest, associated outcomes such as psychiatric symptoms and cognition were secondary and not always reported and treatment effects were quantitively assessed using end-of-treatment data due to heterogeneity in follow-up periods, so enduring effects of NM interventions were unable to be adequately determined, highlighting a need for more controlled and comprehensive trials to validate these preliminary findings.

Relevance:
The C-L psychiatrist will frequently encounter patients with SUDs and may offer pharmacological and/or psychological treatments; however, these treatment options may not always be effective or well-tolerated and patients may be interested in alternatives. NM treatments, such as rTMS, are safe and effective low-risk procedures used for several psychiatric disorders including, but not limited to, major depressive disorder, obsessive-compulsive disorder, and smoking cessation, for which they are also FDA-approved. Given the non-invasive nature of these therapies and their potential for targeting specific brain areas implicated in addiction, NM treatments should NOT be considered as treatments of last resort and C-L psychiatrists should consider advocating for or implementing these interventions to enhance treatment outcomes.