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.