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Re: users preferring 2C-B to MDMA because it doesn't deplete serotonin: I believe depletion of serotonin is thought to be a possible mechanism for the "crash"/brief period of depression that people can experience after MDMA use, especially with frequent or repeated use. Not surprising that people might prefer it, if 2C-B has a similar high without that particular adverse effect.
What you do matters.