Interaction between Warfarin and Melatonin
Moderate Synergy

ID DDInter1951 and DDInter1142
Interaction Limited data suggest that melatonin may potentiate the effects of warfarin. The precise mechanism of interaction has not been established.
Management Patients treated with warfarin may require more frequent monitoring of their INR following initiation or discontinuation of melatonin.
References
Alternative for Warfarin B01A
Desirudin
Dicoumarol
Iloprost
Selexipag
Anistreplase
Abciximab
Defibrotide
Streptokinase
Heparin (flush)
Rivaroxaban
Cangrelor
More
Alternative for Melatonin N05C
Tasimelteon
Dichloralphenazone
Propiomazine
Ramelteon
Remimazolam
Scopolamine
Valerian
Suvorexant
Quazepam
Scopolamine (ophthalmic)
Eszopiclone

Potential Metabolism Interactions

Substrate-Substrate Interaction：If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction：Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction：Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.