Senna tea addiction is a form of bulimia. I know this because my dear friend went through this. It took a long time for her to even realize that what she was doing was binging and purging but that's what it is. It would be good idea for you to get help and support for this. In this situation it seems that doing the mc might be another version of purging.
I lost my dear friend last summer and it seems that her untimely passing was at least in part due to her abuse of laxitive (senna). She was a wonderful person and I am sure you are too so please think about getting some help with your issue. There are plenty of support groups etc.. that can offer help.