See also Warning section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug include: certain pain medications (mixed opioid agonist-antagonists such as butorphanol, nalbuphine, pentazocine), naltrexone, samidorphan.

Other medications can affect the removal of fentanyl from your body, which may affect how fentanyl works. Examples include azole antifungals (such as itraconazole, ketoconazole), calcium channel blockers (such as diltiazem, verapamil), HIV protease inhibitors (such as nelfinavir), macrolide antibiotics (such as erythromycin), mifepristone, nefazodone, rifamycins (such as rifabutin), ritonavir, certain drugs used to treat seizures (such as carbamazepine, phenytoin), among others.

Taking MAO inhibitors with this medication may cause a serious (possibly fatal) drug interaction. Avoid taking MAO inhibitors (isocarboxazid, linezolid, metaxalone, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, safinamide, selegiline, tranylcypromine) during treatment with this medication. Most MAO inhibitors should also not be taken for two weeks before treatment with this medication. Ask your doctor when to start or stop taking this medication.

The risk of serious side effects (such as slow/shallow breathing, severe drowsiness/dizziness) may be increased if this medication is used with other products that may also cause drowsiness or breathing problems. Tell your doctor or pharmacist if you are taking other products such as other opioid pain or cough relievers (such as codeine, hydrocodone), alcohol, marijuana (cannabis), drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy or cough-and-cold products) because they may contain ingredients that cause drowsiness. Ask your pharmacist about using those products safely.

The risk of serotonin syndrome/toxicity increases if you are also taking other drugs that increase serotonin. Some examples are street drugs such as MDMA/ "ecstasy," St. John's wort, certain antidepressants (such as SSRIs like fluoxetine/paroxetine, SNRIs like duloxetine/venlafaxine), among others. The risk of serotonin syndrome/toxicity may be more likely when you start or increase the dose of these drugs.

This medication may interfere with certain lab tests (such as amylase/lipase levels), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.