But the studies are pervasive. For example, the (flawed) study that found that one cup of wine with each meal was healthier that no alcohol at all is still quoted today, and still "reproduced" in other studies that make the same claim but adding a clause of "given that you also [do good amount of exercise|eat very healthy|are in perfect health already]". Or the flawed studies that Soffriti and Belpoggi pushed (some of them didn't even pass peer review, but reached the public anyway) about artificial sweeteners and other things being carcinogenic: they basically feed mices with whatever they feel until they die, they look the corpses and if there is a tumor, eureka: what they put in the diet is the cause. Nobody took the studies seriously, except the public that now have a "scientific paper" that says Coca-cola causes breast cancer.
In this case some public reads "smoking a joint daily equals invulnerable to Alzheimer, science says so".
Yup. There's definitely a pattern and it seems like an obvious consequence of the structure of incentives.
If you make a product you can make a study that shows it has some kind of benefit in some specific way, even if it probably causes more harm in other ways that are less obvious, and then you can sell it. Media will spread around your study especially if it shows something that will be a bit click-baity, and any study or discussion of the possible downsides will get far less attention.
This is also why basically every edible plant has some article saying it's a "super food" etc etc.