MDA: general

MDA's pharmacological and neurochemical profile closely resembles both LSD and amphetamine [1]. Its effects are reported as a mix of stimulant, entactogenic (empathy/connection-promoting), and psychedelic [2]. It's reported to be taken chiefly by mouth [2]. Compared with MDMA, it's reported to be more psychedelic and less empathogenic [3].

It was first synthesized in 1910 [4][5]; its psychoactivity is reported to have been discovered by American chemist Gordon Alles, who took it himself in 1930 [5][4]. Between 1949 and 1957, Smith, Kline & French gave it to more than five hundred human subjects while investigating it as an antidepressant and appetite suppressant [4], and companies are reported to have tested it for Parkinson's disease, depression, obesity, and cough [5]. During separate testing with MDA and related compounds in 1952–53, an unwitting patient died, and this was kept from the public [6]. The U.S. military is also reported to have investigated it as a possible interrogation drug under the codename EA-1298 [5].

MDA is reported to have emerged as a recreational drug in the late 1960s, before MDMA became popular [3]. It's been reported to have potential as a psychotherapeutic tool, alongside MDMA [7] — but reported potential is not the same as an established safety margin, and nothing here tells you a dose, a duration, or how it interacts with anything else you might take.

References

1. 3,4-Methylenedioxyamphetamine - Expert Committee on Drug Dependence Information Repository — WHO / UN Commission on Narcotic Drugs
2. MDA (drug) — Wikipedia
3. MDA: Dosage, Effects & Safety — Effect Index
4. 3,4-Methylenedioxyamphetamine — Wikipedia
5. MDA: What is MDA, the Sass Drug, and MDA vs. MDMA — DoubleBlind Mag
6. MDA, MDMA, and other 'mescaline-like' substances in the US military's search for a truth drug (1940s to 1960s) — Drug Testing and Analysis (Wiley)
7. An exploration of the history and controversies surrounding MDMA and MDA — PubMed / NIH