I have dealt with neighbor issues before for different reasons(dogs). It can turn to a PITA quickly.
Go talk to him in a considerate and mature manner. He may not even realize that his habit is affecting others and give him an opportunity to correct the situation. Document the conversation.
Document dates and times you notice the stank.
If he does not correct it or gets snotty then go to the HOA with a written complaint. More than likely there is an "Illegal activity" or "drug" prohibition in the by-laws. Document this and the HOA response.
If it turns out he is a MMJ cardholder it may complicate it a bit but you still have an edge. While he may have the right to use his "medicine" he does not have the right to be a nuisance to others when he "medicates". If you have to take this to a LE level have your ducks in a row and be able to show that you have taken "reasonable means" to address the situation. This is why you document everything.
If LE won't do anything as far as pursuing the Ganja angle then you need to push the Nuisance/Disturbing the Peace angle.

Most importantly keep your cool, never retaliate or threaten him. Neighbor issues are tough and it can become a "who can last the longest" situation.
You lose your cool, you lose your edge and credibility.