^
I agree. Apart from causing a bad experience, lithium is also serotonergic, and I don't know if this could lead to serotonin toxicity but it's possible. Someone with knowledge of the pharmacology of lithium could perhaps shed some light on this. It's also not advised to take MDMA when you have mental issues, amphetamines can cause a manic state in people with BPD, as well as increasing other symptoms. Also not much is known about this combo so there's no telling what other interactions between MDMA and lithium we do not yet know of
Have you tested your MDMA with a testkit? I'll add the (untested) prefix, if you did test your drugs let me know. Also if you, against advice, decide to go through with this, start very very low. Better to not feel anything and to increase the dose in the next roll than to take too much and causing a bad experience. But again, I wouldn't risk it, there are too many factors that could cause a negative reaction I think