The risk or severity of adverse effects can be increased when Isoflurane is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Aprepitant. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ziconotide. 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 Fentanyl is combined with Dextromoramide. Fentanyl may increase the bradycardic activities of Metipranolol. The serum concentration of Fentanyl can be increased when it is combined with Saquinavir. The risk or severity of adverse effects can be increased when Imipramine is combined with Fentanyl. The therapeutic efficacy of Pegvisomant can be decreased when used in combination with Fentanyl. The serum concentration of Prucalopride can be increased when it is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Talinolol. 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 Ethylmorphine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Brotizolam. The risk or severity of adverse effects can be increased when Hydromorphone is combined with Fentanyl. 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 Pipotiazine. 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 Palbociclib. The risk or severity of adverse effects can be increased when Fentanyl is combined with Tiagabine. The serum concentration of Fentanyl can be increased when it is combined with Telithromycin. The serum concentration of Fentanyl can be increased when it is combined with Voriconazole. Fentanyl may increase the bradycardic activities of Alprenolol. Fentanyl may increase the bradycardic activities of Atenolol. 7,8-Dichloro-1,2,3,4-tetrahydroisoquinoline 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 Bifeprunox. The serum concentration of Fentanyl can be decreased when it is combined with Midodrine. The serum concentration of Fentanyl can be increased when it is combined with Posaconazole. The risk or severity of adverse effects can be increased when Chlorpromazine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Tolterodine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Buspirone is combined with Fentanyl. The serum concentration of Silodosin can be increased when it is combined with Fentanyl. 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 Fentanyl is combined with Chlorzoxazone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Butethal. The risk or severity of adverse effects can be increased when Homatropine is combined with Fentanyl. 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 Clonazepam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Paliperidone. Granisetron may increase the serotonergic activities of Fentanyl. The risk or severity of adverse effects can be increased when Loxapine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Alprazolam is combined with Fentanyl. Hydracarbazine 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 Butorphanol is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Fosphenytoin. 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 Atorvastatin. Fentanyl may increase the bradycardic activities of Platelet Activating Factor. The serum concentration of Fentanyl can be increased when it is combined with Nilotinib. The risk or severity of adverse effects can be increased when Fentanyl is combined with Harmaline. The risk or severity of adverse effects can be increased when Methscopolamine is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Vemurafenib. The risk or severity of adverse effects can be increased when Fentanyl is combined with Canrenone. The risk or severity of adverse effects can be increased when Pirenzepine is combined with Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Rifapentine. 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 Fentanyl is combined with Enflurane. 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 Thioproperazine. The risk or severity of adverse effects can be increased when Vecuronium is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethotoin. The serum concentration of Fentanyl can be decreased when it is combined with Bosentan. Fentanyl may increase the central nervous system depressant (CNS depressant) activities of Paraldehyde. 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 Pizotifen. The serum concentration of Fentanyl can be increased when it is combined with Ticlopidine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Piretanide. Iproclozide 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 Asenapine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Fluticasone propionate. The risk or severity of adverse effects can be increased when Fentanyl is combined with Almotriptan. Nabilone 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 Flunitrazepam. The risk or severity of adverse effects can be increased when Fentanyl is combined with Perphenazine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Clomipramine. 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 Fentanyl is combined with Ergoloid mesylate. The serum concentration of Rosuvastatin can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Dezocine. 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 Olanzapine is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Nelfinavir. The serum concentration of Fentanyl can be increased when it is combined with Atazanavir. Chlorphentermine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Pergolide is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Zonisamide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methaqualone. 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 Dimenhydrinate. 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 Fentanyl is combined with Norflurane. The risk or severity of adverse effects can be increased when Fentanyl is combined with Entacapone. The risk or severity of adverse effects can be increased when Fentanyl is combined with Efavirenz. The risk or severity of adverse effects can be increased when Fentanyl is combined with Procarbazine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Torasemide. Methamphetamine may increase the analgesic activities of Fentanyl. The serum concentration of Cerivastatin can be increased when it is combined with Fentanyl. Ammonium chloride may increase the excretion rate of Fentanyl which could result in a lower serum level and potentially a reduction in efficacy. The risk or severity of adverse effects can be increased when Tramadol is combined with Fentanyl. Pivhydrazine 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 Umeclidinium is combined with Fentanyl. 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 Moclobemide. Minocycline may increase the central nervous system depressant (CNS depressant) activities of Fentanyl. Fentanyl may increase the bradycardic activities of Bupranolol. The serum concentration of Fentanyl can be increased when it is combined with Lovastatin. Pargyline 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 Benactyzine is combined with Fentanyl. Tropisetron may increase the serotonergic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Mersalyl. The risk or severity of adverse effects can be increased when Pentazocine is combined with Fentanyl. Doxylamine 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 Diazepam. The serum concentration of Fentanyl can be increased when it is combined with Dasatinib. 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 Deramciclane. Perampanel may increase the central nervous system depressant (CNS depressant) activities of Fentanyl. The risk or severity of adverse effects can be increased when Tubocurarine is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Arotinolol. 2,5-Dimethoxy-4-ethylamphetamine may increase the analgesic activities of Fentanyl. 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 Fentanyl is combined with Selegiline. The serum concentration of Fentanyl can be increased when it is combined with Nevirapine. 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 Quazepam. The serum concentration of Fentanyl can be increased when it is combined with Sildenafil. The risk or severity of adverse effects can be increased when Fentanyl is combined with Pomalidomide. Fentanyl may increase the central nervous system depressant (CNS depressant) activities of Zolpidem. 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 Methylphenobarbital.