Background: Intensified by influence of media there is an enormous trend towards additionally natural self-medication e.g. to cure with teas and drugs of natural resources seeming to be harmless even in most physiciansÂ'opinion. The transplant patient is at high risk to be affected by this modern way of co-treatment as well. E.g. we all are familiar with the herb-drug interaction resulting from St. John's wort. Experience and case report: In clinical pharmacology we are increasingly confronted with the question whether special natural agents the patients intend or started to supply themselves with in order to support or detox their existing medication may be associated with interactive potential. Esp. concerning therapeutic drug monitoring for immunosuppressants this aspect always needs being aware of. There are numerous natural agents we checked in detail via available literature throughout the last years concerning this problem. From these data it is recommended to be more cautious than most patients and physicians tend to be. Most of the agents are classified as safe concerning interactions despite lacking data whether they have been checked adequately or not. As an impressive own example we report on our recent finding in a male patient (P) 24yrs of age being within the earliest very sensitive phase of hematopoietic stemcell transplantation. He is on a standard therapeutic regimen including cyclosporine (CSA) achieving stable trough levels within therapeutic range (˜ 250ng/ml) with a twice daily dosage of 175mg intravenously. On day 4 his CSA trough level decreases to subtherapeutic132ng/ml, daily increasing dose adjustment becomes necessary to recover from this severe decrease and there is no agent within comedication that can be identified to be responsible for this phenomenon e.g. as an enzyme inducer. Our insisting inquiries at least reveal the P himself started to drink concentrated sage tea (salve) to overcome severe mucositis induced by preceeding conditioning regimen. To achieve therapeutic CSA trough levels the dosage almost needs being doubled (1.9 fold; 325 mg intravenously twice daily = 650mg vs. 350 mg/day). Without any evidence from literature we ask to stop ingestion of sage tea yet. This intervention results in increasing CSA exposure again as the P presented prior to sage consumption indicating recovering from sage-CSA interaction. The close drug-monitoring again documents to be the only reliable indicator to enable earliest adaption in decreasing trough blood levels of immunosuppressants as CSA which in this context is regarded as being almost entirely checked concerning clinically relevant drug-drug or herb-drug interactions. It might have protect the P from graft versus host disease or even lethal failure of engraftment. Conclusion: 1. It is a recommending challenge always to search for the reason for inadequate alterations of trough blood levels. 2. Sage seems to have an interactive potential with CSA. 3. Further investigation of sage which includes more than 60 ingredients is required to elucidate the mode of sage-CSA interaction e.g. via CYP3A4 inducer or P-glycoprotein or both resp. 4. This mechanism probably might be the same with tacrolimus and mTORinhibitors because of their analogous metabolism.