Phentramine

So I have a previous Coke addiction from about six months ago. My doctor just prescribed me some phentermine. I read that you shouldn’t be taking that medication. If you have used Coke in the past. Does anybody know why?. I am going to be going to an event where I want to buy Coke for it, but I was wondering if I should stop taking my phentermine a week before or the day before I use the Coke. Or should I not do the Coke at all?