Ketamine is probably what you're thinking of. Not as bad, it's pretty addictive (but so is adderal, go figure). From what I'm aware, if you want concentration you would need pretty small doses of ketamine as it's mostly a downer. The other thing though is that you can't do ketamine habitually for a long time because it really fucks up your bladder.

Low dosage ketamine IV treatment has some promising early results, especially with extreme ADHD symptoms or comorbidity with depression/anxiety, and lasts longer than the current injection methods.

I know it's pretty inaccessible depending where you live in the world, but if you have any places around you that are doing research trials of this, I would highly recommend signing up. Not only do you get to try the treatment in a controlled environment, you contribute more data to the pool for eventual large scale treatment methods.