One point that hasn't been addressed so far is how misleading this study is. It's looking at death rates related to prescription painkiller deaths doing a time-series analysis 1999-2010 and then correlating results to states that made medical marijuana legal over that time period. It doesn't say how they eliminated any other number of causes during that period. This is merely showing correlation not causation.
Most of the examples given in the comments here are anecdotal. Not that I disagree with the overall tone, but this is not the study to hold up and say "This is why we should legalize"
No one implied causation. The study found that states who legalized medical marijuana found a decrease in opium mortality but roughly 20% after 2 years. Around the country, opium mortality rates are increasing. Thus it is quite reasonable to say 'the opium mortality rate is statistically significantly less in medical marijuana states than in others.' No one has claimed anything more than that, and it is in fact science.
As an example people who have more sex make the most money. While we would all like that to be true there's no science proving causation http://blogs.scientificamerican.com/roots-of-unity/sex-makes...
Most of the examples given in the comments here are anecdotal. Not that I disagree with the overall tone, but this is not the study to hold up and say "This is why we should legalize"