Which dietary supplement combined with contingency management has shown to reduce cannabis use?

The correct answer highlights the combination of 2400 mg of N-acetylcysteine (NAC) with contingency management as beneficial in reducing cannabis use. NAC is an antioxidant and mucolytic agent that has been studied for its potential in treating various substance use disorders, including cannabis dependence. Research suggests that NAC may help reduce cravings and withdrawal symptoms associated with cannabis use, likely due to its role in modulating glutamate levels and providing neuroprotective effects.

In the context of contingency management, which is a behavioral intervention that provides rewards for achieving certain goals (such as abstinence from cannabis), the combination with NAC can enhance the effectiveness of the treatment. The incorporation of NAC may support patients in maintaining abstinence, as it acts on neurological pathways involved in addiction.

This scientific background supports why this specific combination has been shown to be effective in studies aimed at reducing cannabis use, making it the correct choice in this scenario.