The metabolism of Levothyroxine can be decreased when combined with Fosamprenavir. Levothyroxine may increase the arrhythmogenic activities of Doxepin. The serum concentration of Levothyroxine can be increased when it is combined with Simeprevir. The metabolism of Levothyroxine can be decreased when combined with Clemastine. The metabolism of Levothyroxine can be decreased when combined with Dronedarone. The metabolism of Levothyroxine can be decreased when combined with Itraconazole. The metabolism of Levothyroxine can be decreased when combined with Delavirdine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Levomilnacipran. The serum concentration of Levothyroxine can be decreased when it is combined with Colesevelam. Levothyroxine may increase the arrhythmogenic activities of Protriptyline. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Genistein. The serum concentration of Vincristine can be decreased when it is combined with Levothyroxine. The serum concentration of Levothyroxine can be decreased when it is combined with Ciprofloxacin. The serum concentration of Dabigatran etexilate can be decreased when it is combined with Levothyroxine. Levothyroxine may increase the arrhythmogenic activities of Amineptine. Levothyroxine may increase the arrhythmogenic activities of Esmirtazapine. The metabolism of Levothyroxine can be decreased when combined with Lovastatin. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Equol. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Calcium Phosphate. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Alaproclate. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Milnacipran. The serum concentration of Levothyroxine can be decreased when it is combined with Mitotane. The serum concentration of Levothyroxine can be decreased when it is combined with Lanthanum carbonate. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Mestranol. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Promestriene. The metabolism of Dyphylline can be increased when combined with Levothyroxine. The metabolism of Levothyroxine can be decreased when combined with Lopinavir. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Desvenlafaxine. The serum concentration of Levothyroxine can be decreased when it is combined with Fosphenytoin. Raloxifene can cause a decrease in the absorption of Levothyroxine resulting in a reduced serum concentration and potentially a decrease in efficacy. Levothyroxine may increase the arrhythmogenic activities of Opipramol. The serum concentration of Levothyroxine can be increased when it is combined with Palbociclib. The serum concentration of Levothyroxine can be decreased when it is combined with Magnesium salicylate. The metabolism of Levothyroxine can be decreased when combined with Venlafaxine. The metabolism of Levothyroxine can be decreased when combined with Rucaparib. The serum concentration of Levothyroxine can be increased when it is combined with Stiripentol. Levothyroxine may increase the arrhythmogenic activities of Dosulepin. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Sarilumab. The metabolism of Ambroxol acefyllinate can be increased when combined with Levothyroxine. Levothyroxine may increase the anticoagulant activities of Acenocoumarol. Levothyroxine may increase the arrhythmogenic activities of Desipramine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Escitalopram. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Estriol. The metabolism of Aminophylline can be increased when combined with Levothyroxine. The metabolism of Levothyroxine can be decreased when combined with Ketoconazole. The serum concentration of Doxorubicin can be decreased when it is combined with Levothyroxine. Levothyroxine may increase the anticoagulant activities of Warfarin. The metabolism of Levothyroxine can be decreased when combined with Erythromycin. The serum concentration of Levothyroxine can be decreased when it is combined with Orlistat. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Hexestrol. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Diethylstilbestrol. The serum concentration of Levothyroxine can be decreased when it is combined with Magnesium Sulfate. The serum concentration of Levothyroxine can be decreased when it is combined with Tocilizumab. The serum concentration of Levothyroxine can be decreased when it is combined with Sevelamer. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Sertraline. The serum concentration of Ledipasvir can be decreased when it is combined with Levothyroxine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Ethinyl Estradiol. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Estradiol. The metabolism of Levothyroxine can be decreased when combined with Atazanavir. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Quinestrol. Levothyroxine may increase the arrhythmogenic activities of Clomipramine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Calcium lactate. Levothyroxine may increase the anticoagulant activities of Dicoumarol. The metabolism of Levothyroxine can be decreased when combined with Dihydroergotamine. The metabolism of Levothyroxine can be decreased when combined with Ranolazine. The metabolism of Levothyroxine can be decreased when combined with Indinavir. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Calcium Gluceptate. The serum concentration of Levothyroxine can be decreased when it is combined with Sucralfate. Levothyroxine may increase the anticoagulant activities of Fluindione. The serum concentration of Levothyroxine can be increased when it is combined with Aprepitant. The metabolism of Theophylline can be increased when combined with Levothyroxine. The risk or severity of adverse effects can be increased when Piracetam is combined with Levothyroxine. Levothyroxine may increase the arrhythmogenic activities of Mirtazapine. The serum concentration of Levothyroxine can be increased when it is combined with Osimertinib. The serum concentration of Afatinib can be decreased when it is combined with Levothyroxine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Chlorotrianisene. The serum concentration of Levothyroxine can be decreased when it is combined with Tolevamer. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Estrogens, esterified. The metabolism of Levothyroxine can be decreased when combined with Telithromycin. Levothyroxine may increase the arrhythmogenic activities of Amoxapine. The serum concentration of Levothyroxine can be increased when it is combined with Fosaprepitant. The serum concentration of Levothyroxine can be decreased when it is combined with Vemurafenib. The serum concentration of Levothyroxine can be decreased when it is combined with Magnesium Hydroxide. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Tibolone. The serum concentration of Levothyroxine can be decreased when it is combined with Rifampicin. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Calcium Acetate. The serum concentration of Levothyroxine can be decreased when it is combined with Polaprezinc. The metabolism of Levothyroxine can be decreased when combined with Posaconazole. The metabolism of Levothyroxine can be decreased when combined with Clotrimazole. The metabolism of Levothyroxine can be decreased when combined with Voriconazole. The metabolism of Levothyroxine can be increased when combined with Rifabutin. The metabolism of Levothyroxine can be decreased when combined with Isavuconazonium. The serum concentration of Levothyroxine can be decreased when it is combined with Aluminum hydroxide. The serum concentration of Levothyroxine can be decreased when it is combined with Cholestyramine. The metabolism of Levothyroxine can be decreased when combined with Bortezomib. The serum concentration of Levothyroxine can be increased when it is combined with Dasatinib. The metabolism of Levothyroxine can be decreased when combined with Nefazodone. The metabolism of Levothyroxine can be decreased when combined with Atomoxetine. The metabolism of Levothyroxine can be decreased when combined with Imatinib. The serum concentration of Levothyroxine can be increased when it is combined with Ceritinib. Levothyroxine may increase the arrhythmogenic activities of Tianeptine. The serum concentration of Levothyroxine can be decreased when it is combined with Deferasirox. The serum concentration of Levothyroxine can be increased when it is combined with Mifepristone. The serum concentration of Levothyroxine can be decreased when it is combined with Magnesium oxide. The metabolism of Levothyroxine can be decreased when combined with Sildenafil. Levothyroxine may increase the anticoagulant activities of Phenprocoumon. The metabolism of Levothyroxine can be increased when combined with Nevirapine. The metabolism of Levothyroxine can be decreased when combined with Fluconazole. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Synthetic Conjugated Estrogens, A. The serum concentration of Levothyroxine can be increased when it is combined with Netupitant. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Calcium Chloride. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Indalpine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Secoisolariciresinol. The serum concentration of Amodiaquine can be increased when it is combined with Levothyroxine. The metabolism of Levothyroxine can be increased when combined with Pentobarbital. The serum concentration of Brentuximab vedotin can be decreased when it is combined with Levothyroxine. The serum concentration of Levothyroxine can be decreased when it is combined with St. John's Wort. The metabolism of Levothyroxine can be decreased when combined with Amiodarone. The metabolism of Levothyroxine can be decreased when combined with Olaparib. The metabolism of Levothyroxine can be decreased when combined with Cobicistat. The metabolism of Levothyroxine can be decreased when combined with Fluvoxamine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Conjugated estrogens. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Duloxetine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Fluoxetine. The serum concentration of Levothyroxine can be decreased when it is combined with Bosentan. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Dapoxetine. Levothyroxine may increase the arrhythmogenic activities of Cyclobenzaprine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Paroxetine. The therapeutic efficacy of Iodide I-131 can be decreased when used in combination with Levothyroxine. The therapeutic efficacy of Levothyroxine can be decreased when used in combination with Calcium Citrate.