Will poor mental health have a substantial negative impact on my progress?

Preface: I know mental health should be my priority, and I am working on it, but if I'm going to be depressed I may as well be jacked and depressed.

I have had various people throughout my life tell me that high levels of stress kill gains, similarly to how it can impact skin/similar. I'm sure this is true to a certain degree, but has anyone had experiences where an actually significant impact was observed? I'd like to pursue fitness once again in my life, and I don't expect my poor mental health to be an issue in that goal, but I'm curious nonetheless.

Note: By "poor mental health" I don't mean low motivation (which would likely lead to missed workouts), but rather primarily high levels of stress (like many people experience with OCD).