Cannabis plus alcohol is one of the most frequently detected drug combinations in car accidents, yet the interaction of these two compounds is still poorly understood.  A study shows for the first time that the simultaneous use of alcohol and cannabis produces significantly higher blood concentrations of cannabis’ main psychoactive constituent, THC, as well as THC’s primary active metabolite than cannabis use alone.

https://www.aacc.org/media/press-release-archive/2015/alcohol-combined-with-cannabis-significantly-increases-levels-of-thc-in-the-blood