I cannot speak from experience but I've heard that some strains of medical marijuana can assist with ADHD as well as relieve pain caused by cancer and lack of appetite caused by chemo. It would be a Sativa strain (Not Indica) and it could be bought as tincture. A tincture is a liquid form of the medication that comes in a little bottle that has an eye dropper. It can give a precise dose. No smoking required. Google it and you should come up with a wealth of information on the subject.
I too have ADD and am just beginning to experiment with medical marijuana to see what works best. If I find a good strain (there are hundreds) I'll pm you. Even without the ADD issues it would still be a good idea to take medical marijuana by any cancer or post cancer patient.
There are non-psychoactive strains of marijuana that have been bred just to ease pain but without the high. Charlotte's Web is one of those strains. That particular strain does not do anything for ADD though.
Check this out for starters: https://www.leafly.com/news/strains-products/best-cannabis-strains-for-focus-and-addadhd.
PS: I would stay away from "conventional" medications, like Adderall which are highly addictive.