People who take oxycodone need to be careful when also taking antifungal drugs or drinking grapefruit juice. Why? Because both the juice and the drug can result in abnormally high, perhaps dangerously so, oxycodone blood levels. The same goes for fentanyl. But people taking morphine or Dilaudid don't have to worry; neither the juice nor the antifungal drug will have a significant effect on the opioid levels. Believe it or not, this all makes sense.