Diminution des concentrations plasmatiques de fentanyl par augmentation de son métabolisme hépatique par la rifampicine.Re: Seriously Freaked Out!! Fentanyl OD or W/D, Not sure! Need to have Guidance!! I am a bit anxious for you. To me it appears like you might not be that opiod tolerant and you also are experiecing some side effects that a lot o