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 Oxitropium is combined with Fentanyl. Palonosetron may increase the serotonergic activities of Fentanyl. 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 Amobarbital. The risk or severity of adverse effects can be increased when Fentanyl is combined with Clidinium. The serum concentration of Fentanyl can be increased when it is combined with Palbociclib. The serum concentration of Fentanyl can be decreased when it is combined with Rilpivirine. Methamphetamine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Propericiazine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Diphenoxylate. The risk or severity of adverse effects can be increased when Fentanyl is combined with 7-Nitroindazole. 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 Aclidinium is combined with Fentanyl. The risk or severity of adverse effects can be increased when Trihexyphenidyl is combined with Fentanyl. Ritobegron may increase the analgesic activities of Fentanyl. BL-1020 may increase the hypotensive activities of Fentanyl. The serum concentration of Fentanyl can be decreased when it is combined with Cirazoline. Phenoxypropazine may increase the central nervous system depressant (CNS depressant) and hypertensive activities of Fentanyl. Magnesium Sulfate may increase the central nervous system depressant (CNS depressant) activities of Fentanyl. Safrazine may increase the central nervous system depressant (CNS depressant) and hypertensive activities of Fentanyl. 3,4-Methylenedioxyamphetamine may increase the analgesic activities of Fentanyl. Ondansetron may increase the serotonergic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Tasimelteon. 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 Propofol. The risk or severity of adverse effects can be increased when Butorphanol is combined with Fentanyl. 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 Fentanyl is combined with Zotepine. 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 Dyclonine. The serum concentration of Fentanyl can be increased when it is combined with Ritonavir. The serum concentration of Fentanyl can be decreased when it is combined with Tocilizumab. The serum concentration of Fentanyl can be decreased when it is combined with Enzalutamide. The serum concentration of Fentanyl can be increased when it is combined with Nilotinib. The serum concentration of Fentanyl can be increased when it is combined with Netupitant. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ropivacaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Chloroprocaine. Fentanyl may increase the bradycardic activities of Bevantolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Selegiline. Phentermine may increase the analgesic activities of Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Etidocaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Oxazepam. Toloxatone 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 Tramadol is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Potassium Citrate. The risk or severity of adverse effects can be increased when Fentanyl is combined with Azosemide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Methylecgonine. 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 Tiotropium is combined with Fentanyl. Fentanyl may increase the central nervous system depressant (CNS depressant) activities of Methotrimeprazine. 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 Linezolid is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Lamotrigine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Topiramate. The serum concentration of Pazopanib can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Asenapine. The serum concentration of Fentanyl can be decreased when it is combined with Phenytoin. The risk or severity of adverse effects can be increased when Fentanyl is combined with Tizanidine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Metaxalone. The therapeutic efficacy of Pegvisomant can be decreased when used in combination with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Carbinoxamine. The risk or severity of adverse effects can be increased when Methohexital is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Doxepin. 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 Azelastine. 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 Fentanyl is combined with Etacrynic acid. The risk or severity of adverse effects can be increased when Fentanyl is combined with Oxethazaine. The therapeutic efficacy of Fentanyl can be increased when used in combination with Pregabalin. The serum concentration of Fentanyl can be increased when it is combined with Crizotinib. 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 Fentanyl is combined with Ethosuximide. The serum concentration of Fentanyl can be increased when it is combined with Ombitasvir. The risk or severity of adverse effects can be increased when Fentanyl is combined with Butalbital. 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 Quinidine is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Tetracaine. Fentanyl may increase the sedative activities of Pramipexole. The risk or severity of adverse effects can be increased when Fentanyl is combined with Mepivacaine. The serum concentration of Everolimus can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Olopatadine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ecopipam. The serum concentration of Fentanyl can be increased when it is combined with Luliconazole. The serum concentration of Tolvaptan can be increased when it is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Propranolol. The serum concentration of Fentanyl can be increased when it is combined with Venlafaxine. The serum concentration of Fentanyl can be decreased when it is combined with Primidone. 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 Ziconotide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethylmorphine. Fentanyl may increase the bradycardic activities of Metoprolol. 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 Moclobemide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Desflurane. The risk or severity of adverse effects can be increased when Benzatropine is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Olaparib. The risk or severity of adverse effects can be increased when Fentanyl is combined with Triflupromazine. The risk or severity of adverse effects can be increased when Fentanyl is combined with clomethiazole. The risk or severity of adverse effects can be increased when Fentanyl is combined with Propoxycaine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethyl chloride. 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 Fentanyl is combined with Nitrazepam. 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 Fentanyl is combined with Ritanserin. The risk or severity of adverse effects can be increased when Fentanyl is combined with Melatonin. The risk or severity of adverse effects can be increased when Fentanyl is combined with Ethoxzolamide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Cyclopenthiazide. Fentanyl may increase the bradycardic activities of Bufuralol. Minaprine 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 Mecamylamine is combined with Fentanyl. The serum concentration of Simvastatin can be increased when it is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Carisoprodol. The risk or severity of adverse effects can be increased when Clorazepate is combined with Fentanyl. 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 Alfentanil is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Almotriptan. The risk or severity of adverse effects can be increased when Fentanyl is combined with Cariprazine. The risk or severity of adverse effects can be increased when Fentanyl is combined with Fluspirilene. The risk or severity of adverse effects can be increased when Codeine is combined with Fentanyl. Fentanyl may increase the bradycardic activities of Betaxolol. The risk or severity of adverse effects can be increased when Fentanyl is combined with Metoclopramide. The risk or severity of adverse effects can be increased when Fentanyl is combined with Lorcaserin. 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 Metergoline 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 Sufentanil is combined with Fentanyl. The risk or severity of adverse effects can be increased when Fentanyl is combined with Piretanide. The risk or severity of adverse effects can be increased when Vilazodone is combined with Fentanyl. The serum concentration of Fentanyl can be increased when it is combined with Stiripentol.