There was also a pretty famous study w/ mice I believe. One of them had a good world w/ plenty of food, plenty of toys to play with and ample people to hang out with and have sex with. They had two feeding tubes, one contained drugs and other didn't. The mouse repeatedly took the drug free version. Then they created a shit mouse world. I think it was just overcrowded and didn't have any toys or that shit they borrow in. Low and behold the mouse in the shit world chose the feeding tube w/ the drugs.
Calling it junk science is probably overly stated. Seems the largest confounding fact is that different strains of rats have different propensities to addictions. I can see why that would be a scary thing to look at in humans.
Again, I can't say there isn't something there and to that. I can say that it almost always runs straight to racism. Such that I can understand the refrain from funding a lot of those investigations.