The probability is that , if is anxiety is from not having marajuana, it will be out of his system in three months.
I see no increased risk of cancer for this limited use of butane.
If he was self medicating for anxiety, then his anxiety is going to need to be treated. In fact, treating it would be good in either case.
Long term effects of THC are not established well in terms of negative problems, other than the possibility of cognitive dysfunction on certain tests, but this appears to reverse with non use, over time.
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