Many people have asked me about whether cannabis is a useful treatment for ADHD, as it seems to calm the mind. Up to this point my response has been the Dr. Hallowell tries hard to move his patients away from marijuana use. But now Roberto Olivadia PhD, an ADHD expert affiliated with Harvard Medical School whom I know and greatly respect, has put together a convincing article using the science of the brain and research to date on cannabis use and ADHD. Bottom line is this - cannabis use for ADHD is not a good idea, and particularly for those under 25. This fits with my own experience with clients who smoke marijuana. What I've observed is that if it doesn't interfere directly with their lives (hurting work performance in many cases) it hurts their relationship by becoming a crutch that takes their attention (and motivation) away from managing their ADHD in ways proven to be effective and long lasting.
Olivardia's article can be found here. You should read it if you or your partner has ADHD and currently uses cannabis.