I read your question carefully and I understand your concern. That being said if we are speaking about his recovery from the brain tumor surgery I don t think that either marijuana or smoking will have a big impact. The effects of marijuana on the brain need still further studies. There are indications about changes it can produce, but for long term use ones, don t apply to your worry about the recovery from the surgery in the next months. There is no data to indicate any effect on brain tumor. Smoking, while dangerous as it is one of the main risk factors for stroke, cardiovascular and respiratory disease which can affect the brain in the long term future, carries no short term risk about his recovery. So bottom line while both smoking and marijuana are two dangerous addictions which I strongly recommend him to quit due to their long term use consequences, I don t think you should panic about their current use inhibiting his recovery. Perhaps he should be evaluated and if necessary treated about his depression though. Hope to have been of help to you, feel free to ask further questions.