The risk or severity of adverse effects can be increased when Fentanyl is combined with Pomalidomide. The serum concentration of Fentanyl can be decreased when it is combined with Phenytoin. The serum concentration of Fentanyl can be decreased when it is combined with Primidone. The serum concentration of Fentanyl can be increased when it is combined with Voriconazole. The serum concentration of Fentanyl can be increased when it is combined with Nelfinavir. Fentanyl may increase the bradycardic activities of Nebivolol. Fentanyl may increase the bradycardic activities of Bisoprolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Levocabastine. The risk or severity of adverse effects can be increased when Amoxapine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Cyclopentolate is combined with Fentanyl. The risk or severity of adverse effects can be increased when Methadone is combined with Fentanyl. The risk or severity of adverse effects can be increased when Pergolide is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Crizotinib. The risk or severity of adverse effects can be increased when Fentanyl is combined with Benzocaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Halazepam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Rasagiline. The risk or severity of adverse effects can be increased when Fentanyl is combined with Eplerenone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Articaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dihydromorphine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Etomidate. 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 Oxyphenonium is combined with 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 Fentanyl is combined with Fludiazepam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methapyrilene. The serum concentration of Fentanyl can be increased when it is combined with Dasatinib. The serum concentration of Fentanyl can be increased when it is combined with Ritonavir. The risk or severity of adverse effects can be increased when Fentanyl is combined with Osanetant. The risk or severity of adverse effects can be increased when Vilazodone is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Procarbazine. The serum concentration of Fentanyl can be increased when it is combined with Fluconazole. The risk or severity of adverse effects can be increased when Fentanyl is combined with Melperone. The risk or severity of adverse effects can be increased when Glycopyrronium is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Molindone. Nialamide may increase the central nervous system depressant (CNS depressant) and hypertensive activities of Fentanyl. Fentanyl may increase the bradycardic activities of Sotalol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ecopipam. The risk or severity of adverse effects can be increased when Zolmitriptan is combined with Fentanyl. The serum concentration of Pravastatin can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Etizolam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Opium. The serum concentration of Fentanyl can be increased when it is combined with Nefazodone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Heroin. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ketazolam. Fentanyl may increase the bradycardic activities of Metoprolol. Amphetamine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Metaxalone. The risk or severity of adverse effects can be increased when Oxybutynin is combined with Fentanyl. The therapeutic efficacy of Fentanyl can be decreased when used in combination with Sarilumab. The serum concentration of Doxorubicin can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Halothane. 4-Bromo-2,5-dimethoxyamphetamine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Loprazolam. Dextroamphetamine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Propericiazine. Ondansetron may increase the serotonergic activities of Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Fluvoxamine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Cyclopenthiazide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Maprotiline. The risk or severity of adverse effects can be increased when Alfentanil is combined with Fentanyl. 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 Trospium is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Ceritinib. The serum concentration of Rifaximin can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Isoflurane is combined with Fentanyl. 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 Fentanyl is combined with Ethotoin. 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 Fentanyl is combined with Amisulpride. Methylene blue may increase the hypotensive activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Eltanolone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethyl carbamate. The risk or severity of adverse effects can be increased when Atracurium besylate is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Mepivacaine. The risk or severity of adverse effects can be increased when Benzatropine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Metergoline is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Paliperidone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Pramocaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Pimozide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dextromoramide. The serum concentration of Fentanyl can be decreased when it is combined with Methoxamine. Octamoxin 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 Carfentanil. The risk or severity of adverse effects can be increased when Fentanyl is combined with Agomelatine. 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 Quetiapine. The serum concentration of Fluvastatin can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Clopamide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethosuximide. The risk or severity of adverse effects can be increased when Hyoscyamine is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with St. John's Wort. The risk or severity of adverse effects can be increased when Trimethaphan is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Tocilizumab. The risk or severity of adverse effects can be increased when Fentanyl is combined with Amobarbital. The risk or severity of adverse effects can be increased when Fentanyl is combined with Phenoxyethanol. The risk or severity of adverse effects can be increased when Reserpine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Protriptyline is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Triprolidine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Sulpiride. The risk or severity of adverse effects can be increased when Fentanyl is combined with Alfaxalone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Aripiprazole. The risk or severity of adverse effects can be increased when Fentanyl is combined with Raclopride. Fentanyl may increase the bradycardic activities of Platelet Activating Factor. The risk or severity of adverse effects can be increased when Chlordiazepoxide is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Lidocaine. The risk or severity of adverse effects can be increased when Oxitropium is combined with Fentanyl. The risk or severity of adverse effects can be increased when Codeine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Fluticasone propionate. 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 Pamabrom. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ecgonine. The risk or severity of adverse effects can be increased when Atropine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methsuximide. The risk or severity of adverse effects can be increased when Pethidine is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Carteolol. Fentanyl may increase the bradycardic activities of Atenolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Alphacetylmethadol. Furazolidone 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 Clomipramine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Acetophenazine. The risk or severity of adverse effects can be increased when Methylergometrine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Escitalopram. The risk or severity of adverse effects can be increased when Fentanyl is combined with Carisoprodol. The serum concentration of Topotecan can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Loratadine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Tasimelteon. Fentanyl may increase the bradycardic activities of Bopindolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Almotriptan. Fentanyl may increase the bradycardic activities of Talinolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Nitrous oxide.