I can't in good conscience recommend this treatment to anyone else because my limited understanding is that I am a very rare exception to the general rule that LSD is a very risky thing to take, especially on a regular basis.

Since taking it results in a psychedelic trip, it can be extremely easy for that to backfire and result in a very negative and potentially traumatic experience, commonly referred to as a bad trip.

It's also typically intoxicating; not quite to the level of alcohol, but enough to mess with your sense of balance and ability to speak coherently.

I know this from personal experience - this did not start out as an ADHD treatment for me; it started out as a recreational activity, and required the same amount of investment as psychedelic use typically does. I used to hallucinate (mildly) and be at risk of having a bad trip if anxiety took over. The first time I took this, I had HPPD for the following two weeks; the experience was actually quite comforting for me, but it's important to note that risk as well.

However, over time, even only using it every two to three weeks, my brain gradually became tolerant to its effects. I believe there's some sort of permanent tolerance that isn't documented on PsychonautWiki, which was my primary source of info about the substance; on a couple occasions, I've gone over a month between doses, and it's never quite been as intense as the first time I ever took it, even if I were to take more than before.

I don't know if this happens for everyone. I really do not. I cannot guarantee or even suggest that it would happen to you or anyone if one were to reproduce these steps. There is a lack of study-backed research that exists in this area; this substance really is not especially well understood except by recreational users, and even then, they are only aware of and able to share anecdotes about its effects on themselves individually. Anyone who claims to know whether or not LSD would be safe for you is lying.

But, I will tell you what I am doing, for the express purpose of academic curiosity. Perform your own research into anything that you are ever curious about trying, and please do not take my comment as a suggestion that this will work for you; it would likely not.

I take dextroamphetamine (dexedrine), which I am prescribed for ADHD by my doctor.
I take LSD while this drug is still in my body; that is, I mix them. I started the dexedrine before I ever started taking LSD, but I have always been on dexedrine even while dosing LSD. I find that, on its own, dexedrine does not fully help with the ADHD anymore, at least not like it once did; however, combined with LSD, my brain seems to just work, and I finally feel in full control of my actions.

My doctor is aware that I use LSD in this way. He professionally recommends against it because he cannot guarantee that it is safe, but he understands that I find it helpful. Obviously, you should generally not tell medical professionals that you regularly do illegal drugs; I trust my doctor to a great degree, and he seems to trust me, too.

This more frequent usage (i.e. more frequent than a couple times a month) started slightly over a week ago, when I took this stuff to help myself process the resultant trauma from being hit by a truck and nearly dying about a week prior. It felt incredible to me how much it helped, not only with processing the trauma, but even just with general cognition, language, and executive function; I started taking it about every other day for a couple times, then switched to taking a small non-microdose (100–200μg) every morning. I take my dexedrine in the evening, right before I go to sleep; my dose is 30mg per day.

By the way, without getting into LSD or even alternative medicine in general, it's important to note that different drug manufacturers produce different products even when it's supposed to be the same drug. Actavis/Teva produces dexedrine that I can't take because it immediately puts me into a hypertensive crisis, but Mallinckrodt makes stuff that I can take 30mg/day of and nonetheless maintain a completely normal blood pressure. (My doctor takes it every visit, so he would have told me a long time ago if it were abnormal.)

I would always recommend the prescription route if possible, just because it does lessen the burden on you and it also somewhat lessens your responsibility. I am responsible for my own self, and involving non-prescription drugs means that I need to pay a lot closer attention to their effects in order to ensure that I'm not harming my health. Sometimes this is not worth the effort, especially if the responsibility can't be properly handled for whatever reason.