a diagnosis and previous medication used to be a straight up disqualifier. Over the past few years they’ve slackened that a bit, with some branches going to “unmedicated for a year” or a medical waiver. Ultimately the policies around mental health in recruiting are based around conceptions from the 70s, and given that diagnosis methods have moved on from then, now tending to catch a lot more mild cases, way more people are getting disqualified due to things that used to not be noticed. To be clear, a lot of people currently in the US military today have ADHD, but they weren’t diagnosed until after they were admitted except for very recent recruits.

Part of the reluctance to recruit anyone with any mental health diagnosis is the long shadow of “project 100,000” aka “ McNamara's Folly”. Essentially a program where people who fell in to the bottom 10th percentile of testing on mental and physical were conscripted anyways to make up numbers during the Vietnam war. This lead to some pretty disastrous outcomes, with soldiers conscripted as part of this program dying at 3 times the normal rate. The movie forest gump touches on this a bit, but it kind of glosses over the real tragedy of it all nor the diversity of fucked up situations this created.

The institutional memory of this has created a strong prejudice around any sort of mental health diagnosis in recruits, but again, this is in conflict with the fact that mental health is much less stigmatized these days, and much milder situations that were just ignored in the past are now diagnosed.