The findings of this review support the assertion that opioid antagonists demonstrate promising results in the treatment of disordered or problem gambling (Goslar 2019). Consistent with gambling treatment guidelines in Australia (Thomas 2011), the current review provides preliminary support for the use of opioid antagonists, such as naltrexone and nalmefene, in reducing gambling symptom severity, but not response to treatment. However, this conclusion was based on modest and uncertain evidence that illustrated only short‐term effects of treatment. To date, there is insufficient evidence to ascertain whether effects observed immediately after treatment are maintained. Moreover, because of a lack of evidence, the degree to which these pharmacological agents can improve other indices of gambling or psychological impairment remains unclear. These limitations suggest that, despite recommendations related to the administration of opioid antagonists in the treatment of disordered or problem gambling, these pharmacological interventions should be administered with caution and with careful consideration of patient needs (Thomas 2011). 

The available evidence also suggests potential benefits from olanzapine, an atypical antipsychotic, on gambling symptom severity. However, this conclusion was based on two trials characterised by small samples and evidence of very low certainty. Moreover, given the lack of available evidence, it is unknown whether this beneficial effect extends to other indices of gambling behaviour or psychological functioning. There was also an absence of longer‐term follow‐up evaluation periods. Consequently, additional research is needed before definitive statements regarding the efficacy of atypical antipsychotics such as olanzapine can be made.

The review findings regarding the effects of mood stabilisers (including anticonvulsants) were inconclusive. Although the effect size estimate was indicative of a beneficial effect on gambling symptom severity, it is possible that these interventions were no more effective than placebo; the evidence base is also very small and of very low certainty. Moreover, mood stabilisers do not appear to have a beneficial effect on psychological outcomes, such as depressive and anxiety symptoms. Further research is therefore required to investigate the efficacy of mood‐stabilising agents in the treatment of problem or disordered gambling before any conclusions can be drawn.

There is little evidence for the efficacy of antidepressants in reducing gambling symptom severity, as well as other indices such as gambling expenditure, depressive symptoms, functional impairment, and responder status. As previously suggested, the effect size for antidepressants may fail to cross the threshold for statistical significance due to the smaller samples employed in these trials (Bartley 2013). Moreover, anomalous results from small and less methodologically sound studies seemed to have had an undue influence on the study findings. Trials with larger samples and lower risk of bias are required before any definitive statements regarding the efficacy of antidepressants can be made.

Consistent with the meta‐analysis conducted by Bartley 2013, the findings from this review provide limited support for the efficacy of pharmacological treatments for problem or disordered gambling. The most promising findings are for the efficacy of opioid antagonists, such as naltrexone and nalmefene, and, to a somewhat lesser extent, atypical antipsychotics such as olanzapine, on gambling symptom severity immediately following treatment. A lack of available data precluded the conduct of many meta‐analyses for secondary outcomes, such as other gambling indices and psychological functioning. As such, psychological interventions, namely cognitive‐behavioural therapy and motivational interviewing, remain 'best practice' and the first‐line response for the treatment of gambling problems (Cowlishaw 2012).