Isotopologues, salts, crystalline forms, stereoisomers, of methylone and ethylone and methods of use thereof

Described herein are isotopically enriched analogs of methylone (e.g., deuterated analogs of methylone (e.g., (S)-methylone and (R)-methylone) with improved characteristics. Also described herein are salts (such as hydrochloride salt) and solid forms (e.g., crystalline forms) of methylone. Also described herein are stereoisomers (e.g., enantiomers) of methylone. The present disclosure also provides methods of making and methods of use of the methylone or methylone analogs and solid forms of 3,4-methylenedioxy-N-ethylcathinone hydrochloride described herein to treat brain and neurological disorders such as depression.