Does Ada Protect Me From Being Fired For Prior Drug Use If I Disclose That I'm In Treatment? (ks)

Hi all,
Location: Kansas
I have an employment law question I was hoping someone might be able to help me with. I’ll just start with the question and if you want the full breakdown, please see below.

Q: If I admit to being in a medically assisted drug rehabilitation program, can my employer fire me on suspicion of having been high at work prior to my entering the program? Or would ADA protect me from that as well? (I’ve been clean for almost two years, never disciplined, never received a bad review).

Context:
Several years ago I was addicted to a legal opiate made from Kratom extracts (EDP 7-0H). It was pretty bad. I work at a mid-sized bank. My managers knew, or at least heavily suspected, but never accused me directly and overall treated me fairly, though it obviously put my career on a dead end path and I’d hear comments and get pointed remarks here and there.
I’ve been clean and in a medically assisted recovery program for almost two years now. I’m tested regularly and receive buprenorphine (Sublocade) injections once a month so that even if I took them, opiates wouldn’t work. I’ve made substantial progress at my job and put in a lot of effort to make up for my mistakes, which I believe has been recognized. I believe I was very close to receiving a substantial raise. However, over the last couple weeks those same pointed remarks and side comments have started up again. From what I hear, someone may have found one of those Kratom shots in the bathroom and naturally I’m the prime suspect. It probably doesn’t help that I'm on a stack of medications for some psychological issues, and a recent adjustment has not gone well, leading to some unusual behavior and a significant, but short lived, drop in my performance.
I want to get things back on track if I can. I like my boss, but it’s a professional working relationship. I’m thinking of just having a frank conversation, giving him a broad explanation of my situation, and providing my clean test history and letter from my program administrator without necessarily confessing to anything in the past, though I'll probably have to give some sort of timeline to establish this that this is not a recent change. Just trying to clear the air about what’s going on currently, and hope my mistakes are far enough behind me that I still have a shot at actually making some real progress.

Thank you all in advance.