This seems unsurprising? I'm sure you incur similar risks from smoking or drinking alcohol or large amounts of caffeine on a dailiy basis. The thing is, at least in my small sample size of 10 or so friends who use pot with any frequency, maybe one or two of them use on a daily or near-daily basis. Just about everyone else uses occasionally or socially. This study doesn't seem to make any strong conclusions about this usage pattern, and I would imagine that it's no worse than any other frequently used substance. Again, I don't have a lot of evidence for this beyond anecdotal, but I wouldn't take this as clear evidence that recreational marijuana is doing more harm than good.