Can I smoke marijuana after gastric bypass surgery?

people smoke cigarettes for the nicotine and marijuana for the THC. However, in addition to these chemicals, they get thousands of other chemicals in their bodies from the burning of these plants. Carbon monoxide and numerous other chemicals in the smoke cause vasoconstriction in blood vessels. Because of this and other unknown mechanisms, anastomotic ulcers are common in people who smoke after bypass. These ulcers frequently will not heal until the patient stop smoking. When patients are addicted to smoking they can't stop and therefore some of these ulcers never heal but progress to perforation. This leads to a cascade of problems. I know of many weight-loss surgeons who will not do gastric bypass surgery on someone with even a history of smoking because they are afraid they will restart smoking and the risk of ulceration is so great. 

The ideal would be to stop smoking (regardless of the substance of choice) as it is associated with an awkward post-operative recovery. as you mentioned if this itself predisposes you to cravings, as your eating plan has changed drastically you should take that into account. any disruption in the plan established by your nutritionist could have consequences for your health.

But if smoking is not out of your capacity, you should at least reduce to once a week or at least eliminate the habit for a year while you adapt to the new changes in your diet, adapt your body to physical activity such as going to gym, yoga or activities that help you create a healthy mind-body habit relationship.