According to a study of US jurisdictions published in the October 2018 edition of the International Journal of Drug Policy, those states which have legalised medical marijuana have experienced a rate of workplace fatalities 20% lower than the expected rate among workers aged 25 to 44.

The effect on workers aged 16 to 24 also indicated fewer workplace deaths, but the effect was not statistically significant for that age group.

Correlation is not necessarily causation, of course, and the paper's authors suggest further work is required to understand what is going on. One possibility they raise is that workers who use medical marijuana may have correspondingly reduced their consumption of other drugs.

This group would include alcohol, other recreational drugs, and some prescription medicines.

What do people think of this study, and how plausible is the explanation?