The risk or severity of adverse effects can be increased when Fentanyl is combined with Tiapride. The risk or severity of adverse effects can be increased when Quinidine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Chlorthalidone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Flupentixol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Efavirenz. Phentermine may increase the analgesic activities of Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Lovastatin. The risk or severity of adverse effects can be increased when Fentanyl is combined with Nitrazepam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Pizotifen. The serum concentration of Fentanyl can be decreased when it is combined with Pentobarbital. The risk or severity of adverse effects can be increased when Gallamine Triethiodide is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Mersalyl. Fentanyl may increase the bradycardic activities of Platelet Activating Factor. The serum concentration of Fentanyl can be increased when it is combined with Venlafaxine. The serum concentration of Fentanyl can be increased when it is combined with Ivacaftor. The risk or severity of adverse effects can be increased when Fentanyl is combined with Glutethimide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Estazolam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Drotebanol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Cocaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Sepranolone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Vigabatrin. The serum concentration of Fentanyl can be decreased when it is combined with Cirazoline. The risk or severity of adverse effects can be increased when Fentanyl is combined with Fospropofol. The risk or severity of adverse effects can be increased when Fesoterodine is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Labetalol. Fentanyl may increase the bradycardic activities of Betaxolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Canertinib. The serum concentration of Fentanyl can be increased when it is combined with Conivaptan. The risk or severity of adverse effects can be increased when Chlorphenoxamine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethylmorphine. The risk or severity of adverse effects can be increased when Lysergic Acid Diethylamide is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Tiagabine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Desvenlafaxine. The risk or severity of adverse effects can be increased when Dapoxetine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Baclofen. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dextromoramide. Fentanyl may increase the bradycardic activities of Indenolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Quazepam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethotoin. The serum concentration of Ibrutinib can be increased when it is combined with Fentanyl. Pseudoephedrine may increase the analgesic activities of Fentanyl. Safrazine may increase the central nervous system depressant (CNS depressant) and hypertensive activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methaqualone. The risk or severity of adverse effects can be increased when Amitriptyline is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Trichloroethylene. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methyclothiazide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ergonovine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ziconotide. Fentanyl may increase the bradycardic activities of Alprenolol. The serum concentration of the active metabolites of Dabigatran etexilate can be increased when Dabigatran etexilate is used in combination with Fentanyl. Ondansetron may increase the serotonergic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Lurasidone. The serum concentration of Fentanyl can be increased when it is combined with Fosaprepitant. The risk or severity of adverse effects can be increased when Fentanyl is combined with Trifluoperazine. Fentanyl may increase the central nervous system depressant (CNS depressant) activities of Zolpidem. The risk or severity of adverse effects can be increased when Fentanyl is combined with Triamterene. The risk or severity of adverse effects can be increased when Fentanyl is combined with Theobromine. The risk or severity of adverse effects can be increased when Methadone is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Enzalutamide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Levobupivacaine. The risk or severity of adverse effects can be increased when Propantheline is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Procarbazine. Fentanyl may increase the central nervous system depressant (CNS depressant) activities of Buprenorphine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Canrenoic acid. Fentanyl may increase the bradycardic activities of Nebivolol. The serum concentration of Fentanyl can be increased when it is combined with Boceprevir. The serum concentration of Fentanyl can be decreased when it is combined with St. John's Wort. The serum concentration of Fentanyl can be increased when it is combined with Amiodarone. The risk or severity of adverse effects can be increased when Trimethaphan is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Clonidine. The risk or severity of adverse effects can be increased when Pentolinium is combined with Fentanyl. The risk or severity of adverse effects can be increased when Paroxetine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dyclonine. The therapeutic efficacy of Pegvisomant can be decreased when used in combination with Fentanyl. The serum concentration of Mevastatin can be increased when it is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Mephentermine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Adipiplon. The risk or severity of adverse effects can be increased when Butorphanol is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Rifampicin. Fentanyl may increase the serotonergic activities of Zimelidine. The risk or severity of adverse effects can be increased when Pethidine is combined with Fentanyl. Succinylcholine may increase the bradycardic activities of Fentanyl. Pargyline may increase the central nervous system depressant (CNS depressant) and hypertensive activities of Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Lopinavir. The risk or severity of adverse effects can be increased when Dextromethorphan is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methazolamide. Tapentadol may increase the central nervous system depressant (CNS depressant) activities of Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Metaraminol. The risk or severity of adverse effects can be increased when Haloperidol is combined with Fentanyl. The risk or severity of adverse effects can be increased when Methscopolamine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Rasagiline. Methamphetamine may increase the analgesic activities of Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Clotrimazole. The serum concentration of Fentanyl can be increased when it is combined with Bortezomib. The risk or severity of adverse effects can be increased when Loxapine is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Esmolol. The serum concentration of Pazopanib can be increased when it is combined with Fentanyl. Fentanyl may increase the central nervous system depressant (CNS depressant) activities of Thalidomide. The serum concentration of Rosuvastatin can be increased when it is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Sotalol. The risk or severity of adverse effects can be increased when Sufentanil is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Zotepine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Chlorphenamine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Procaine. The risk or severity of adverse effects can be increased when Metergoline is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Stiripentol. Fentanyl may increase the constipating activities of Eluxadoline. The risk or severity of adverse effects can be increased when Fentanyl is combined with Melatonin. Dronabinol may increase the central nervous system depressant (CNS depressant) activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Indiplon. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dantrolene. Chlorphentermine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methapyrilene. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ketamine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dexmedetomidine. The risk or severity of adverse effects can be increased when Thioridazine is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Pindolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Oxethazaine. The risk or severity of adverse effects can be increased when Imipramine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Hexamethonium is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Nitrous oxide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Nalbuphine. The risk or severity of adverse effects can be increased when Aclidinium is combined with Fentanyl. Thiethylperazine may increase the hypotensive activities of Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Aprepitant. The therapeutic efficacy of Fentanyl can be decreased when used in combination with Naltrexone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Enflurane. Fentanyl may increase the bradycardic activities of Celiprolol. The risk or severity of adverse effects can be increased when Lorazepam is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Pipotiazine.