So, is the implication the one you might expect, that the "gateway drug" effect is real but due to having to buy it from sources that might sell other illegal drugs?

As the team reports, problematic consumption decreased slightly in the group with legal access to cannabis. Consumption is considered problematic if it causes or exacerbates health, social or psychological difficulties—even without dependency in the classic sense.

In particular, a more substantial positive effect through legal access was seen in people who used other drugs in addition to cannabis.

This part is a little confusing, like how do they tell what is the cause of difficulties? Do they mean these people were still buying other black market drugs in addition to getting weed from a pharmacy? If so what would be the reason for the improvement?