Drug abuse and obesity are generally a response to chronic stress. America has a chronic stress epidemic due to our work culture and lack of social safety nets. Philanthropic billionaires are people (or progeny of those) who successfully exploited this system. Ergo, the existence of one is correlated with the other, and they share a common cause.

Has our work culture recently become more stressful or our safety nets diminished?

Both, but probably more of the latter. Since the 70s the entire economy and society has been built for consumption and price optimization. That has resulted in both higher life stresses (more two income working households, most Americans have no savings, etc.) and encouraged politicians to cut safety nets which might have diminished the negative effects.

The Sackler family is directly implicated in the 'drugs' part.