Medical marijuana and risk management

We will soon have medical marijuana availability in our state and probably all states. I should be content with this thrust at libertarian pragmatism with a nod to recent medical science.  But part of me protests. There are potential risks that are seldom mentioned, with all the cultural noise. We know that half the adult population is pro marijuana under any circumstances, and about a third are strongly opposed. I simply have two questions:

Does anyone have any science concerning the combination of low and high doses of marijuana in combination with prescription meds, or alcohol, or other substances?  It would be nice if the advocate groups would follow up legalization with some (voluntary and anonymous) research so shared experiences can be scientifically analyzed in case there is a risk. The research could include secondary cannabis smoke for good measure.

Do we know how to define and measure DUI or impairment with cannabis?  It is all very nice to have people get the benefit of marijuana until we consider the risks of driving a vehicle or operating machinery.  The opponents of medical marijuana could perhaps direct their efforts constructively toward improving the measurement and the calculation of impairment to save accidents.

If there is a third risk, it would be unintended use or overdose.  We think about teenagers (just lock the stuff up) but more serious perhaps is food.  It appears that in many states the consumption of cannabis snacks and goodies is growing faster than other forms.  Getting the strength right on the labeling might be a role for (cough cough) the government regulators.