On the other hand, a study in healthy adults found that concomitant administration of fentanyl did not affect the plasma level of CBD, and the co-administration did not produce cardiovascular complications or respiratory depression during the test sessions and CBD did not potentiate fentanyl effects [48]; however, keloconazole (CYP3A4 inhibitor) was found to increase and rifampin (a CYP3A4 inducer) to reduce THC and CBD concentrations [49]. The gene discussed is CYP3A4; the disease is Respiratory insufficiency due to muscle weakness.