Can I use Fentora if I take verapamil (Calan, Covera, Verelan)?

If you take the blood pressure medicine verapamil (Calan, Verelan) while you're using Fentora (fentanyl), a prescription pill for breakthrough cancer pain, you'll need to be carefully monitored. Verapamil can cause fentanyl -- the active ingredient in Fentora -- to build up in your body, increasing the risk of coma or fatal overdose. You and your doctor should watch for signs of a buildup, such as increased sleepiness or a sighing pattern of breathing (in which a deep breath is followed by a long pause), especially when your dose of Fentora is increased.