I’m assuming you mean doing multiple 19-nors, not nandrolones. Usually this is in reference to doing nandrolone in tandem with trenbolone. I should preface that I’ve not done it, so take it for what it’s worth, but I’ve heard it’s often fine. Sometimes people report a lot of negative mental sides, but that’s always doing to be individual. For some, nandrolone makes them really brooding and depressed. For some, tren makes them really manic and aggressive. Adding the two can make those people manic-depressive, which yeah, isn’t probably very desirable.
I do not think it will generally result in increased prolactin related sides. Prolactin can be mitigated with adequate e2 management, or failing that, a DA like caber. My point is that even if it’s a thing for an individual, that can be mitigated.
The right answer here is to do a low dose of both and see how they impact you personally, since this is all so individual. I do plan on adding tren on the back half of my next nand run. I do not foresee any issues, and think the majority of this is hearsay and broscience. But again I haven’t done it yet to speak to my own personal anecdote yet.