Diminution des concentrations plasmatiques de fentanyl par augmentation de son métabolisme hépatique par la rifampicine.Re: Seriously Freaked Out!! Fentanyl OD or W/D, Undecided! Have to have Guidance!! I am somewhat involved in your case. To me it looks like you may not be that opiod tolerant and you are experiecing some side effects that most o