It is indeed a fact that marijuana currently cultivated in the United States is nearly 3 times the THC concentrations than marijuana grown during the 1960's. The increase in THC content although doesn't translate into a more dangerous drug for patients taking it for medical patients. The vast majority of medical marijuana is consumed through digestion and not through smoking.
Marijuana today is more potent because people know more about how to grow it and have nicer technology to help them do so. That doesn't make it more dangerous to anybody, the people that use it know it's more potent and it's not like they were smoking weed from 1980 up until a week ago and got hit with a batch of the current stuff. Tolerance has adapted to the stronger drug.