Interaction between St. John's Wort and Methylene blue
Major Synergy

ID DDInter1708 and DDInter1186
Interaction Coadministration of methylene blue with serotonergic agents may potentiate the risk of serotonin syndrome, which is a rare but serious and potentially fatal condition thought to result from hyperstimulation of brainstem 5-HT1A and 2A receptors. Current research suggests that methylene blue has structural properties similar to monoamine oxidase inhibitors (MAOIs). As such, it may enhance serotonergic effects by inhibiting serotonin metabolism.
Management Serotonergic agents should not be used in patients receiving methylene blue intravenously. Most serotonergic psychiatric drugs should be stopped 1 to 2 weeks (i.e., 4 to 5 half-lives) prior to treatment with methylene blue if possible, while others such as fluoxetine may require discontinuation up to 5 weeks in advance due to its prolonged half-life.
References
Alternative for St. John's Wort -
Alternative for Methylene blue V03A
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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.