1953 CE
The Army Chemical Center studied MDMA toxicity by giving MDMA to animals

In 1953, the U.S. Army undertook studies to assess the toxicity of mescaline analogues, and MDMA was specifically chosen for these tests because it has strong structural similarities to both amphetamine and mescaline. The Army tested MDMA on guinea pigs, rats, mice, monkeys, and dogs, and concluded that MDMA was less toxic than MDA.

Source: Karch, S. B. (2011). A historical review of MDMA. Open Forensic Science Journal.