Methylone, also known as 3,4-methylenedioxy-N-methylcathinone (MDMC), is an entactogen and stimulant drug of the amphetamine, cathinone, and benzodioxole families related to 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy"). It is the β-keto or cathinone analogue of MDMA. Methylone is usually taken orally, but is also used by other routes.

The drug acts as a serotonin–norepinephrine–dopamine releasing agent (SNDRA). It has much less activity at the vesicular monoamine transporter 2 (VMAT2) than MDMA and may have less serotonergic neurotoxicity. In contrast to certain other entactogens like MDMA, methylone does not appear to be a significant agonist of the serotonin 5-HT₂ receptors. Methylone is similar in its effects to MDMA, producing entactogenic effects and euphoria, but has a reputation of being gentler than MDMA and only lasts about half as long. Side effects of methylone include tachycardia, hangover, and insomnia. It may have reduced negative after-effects compared to MDMA. Methylone's onset is about 0.5 hours and its duration is about 2 to 3 hours.

Methylone was first synthesized by Peyton Jacob III and Alexander Shulgin in the mid-1990s and was first described in the literature in 1996. It was patented by Jacob and Shulgin as a potential antidepressant and antiparkinsonian agent, but was never developed or marketed for such uses. Methylone was encountered as a designer and recreational drug by 2004 and has become a controlled substance in many countries. Similarly to MDMA, it is being developed for the treatment of post-traumatic stress disorder (PTSD).

Methylone substitutes for MDMA in drug discrimination tests in rodents. Methylone does not substitute for the stimulant amphetamine or for the hallucinogen DOM in animal drug discrimination tests. Further, also in common with MDMA, methylone acts on monoaminergic systems. In vitro, methylone has one third the potency of MDMA at inhibiting platelet serotonin accumulation and about the same in its inhibiting effects on the dopamine and noradrenaline transporters.

In spite of these behavioral and pharmacological similarities between methylone and MDMA, the observed subjective effects of both drugs are not completely identical. Alexander Shulgin wrote of the former:

"[Methylone] has almost the same potency of MDMA, but it does not produce the same effects. It has an almost antidepressant action, pleasant and positive, but not the unique magic of MDMA."

In acute pharmacological studies of methylone (50–300 mg) in humans, the drug produced physiological and psychological effects including increased blood pressure, heart rate, body temperature, pupil dilation, stimulation, euphoria, feelings of well-being, enhanced empathy, increased sociability, and altered perception. The studies found that the effects of methylone were similar to or milder than those of MDMA. Methylone had a faster onset of action and its subjective effects wore off sooner than MDMA, which might lead to a redosing pattern of use. The misuse potential of methylone, as measured by for instance drug liking responses, appeared to be similar to that of MDMA. However it also has less off-target effects than MDMA which may be an advantage for medical applications.

Methylone acts as a mixed releasing agent and reuptake inhibitor of serotonin, norepinephrine, and dopamine. In comparison to MDMA, it has approximately 3-fold lower affinity for the serotonin transporter, while its affinity for the norepinephrine and dopamine transporters is similar. Notably, methylone's affinity for the vesicular monoamine transporter 2 (VMAT2) is about 13-fold lower than that of MDMA. The results of these differences in pharmacology relative to MDMA are that methylone is less potent in terms of dose, has more balanced catecholaminergic effects relative to serotonergic, and behaves more like a reuptake inhibitor like methylphenidate than a releaser like amphetamine; however, methylone still has relatively robust releasing capabilities.