Legalizing medical marijuana causes a reduction in painkiller deaths. Even before the recent surge of legalization victories, we had enough data in diverse regions to definitely support the claim without any correlation/causation concerns.

According to a 2014 JAMA study, via Newsweek:

In the 13 states that passed laws allowing for the use of medical marijuana between 1999 and 2010, 25 percent fewer people die from opioid overdoses annually.

This impact is even more impressive when held up against the national trend: annual opioid deaths in America nearly quadrupled between 1999 and 2014.

Among the states that voted to legalize medical marijuana this year, Florida has the most to gain from a reduction in opioid fatalities.

According to the most recent full-year data — collected by the Kaiser Family Foundation — Florida had 1,399 opioid deaths in 2014, more than all but three states (New York, California, Ohio). If Florida sees an impact on par with that detected by the JAMA study, the state can expect to save 350 lives annually from opioid death.