MXE + 4mmc/Mephedrone
Dangerous
There is a high risk of serotonin syndrome from this combination.

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DeLarge, A. F., Erwin, L. L., & Winsauer, P. J. (2017). Atypical binding at dopamine and serotonin transporters contribute to the discriminative stimulus effects of mephedrone. Neuropharmacology, 119, 62–75. https://doi.org/10.1016/j.neuropharm.2017.04.006

Kehr, J., Ichinose, F., Yoshitake, S., Goiny, M., Sievertsson, T., Nyberg, F., & Yoshitake, T. (2011). Mephedrone, compared with MDMA (ecstasy) and amphetamine, rapidly increases both dopamine and 5-HT levels in nucleus accumbens of awake rats: Mephedrone increases both DA and 5-HT in rat brain. British Journal of Pharmacology, 164(8), 1949–1958. https://doi.org/10.1111/j.1476-5381.2011.01499.x