Animal studies indicate that MDMA administration, even at dosages of 0.75-1.5 mg/kg, can lead to a loss of serotonergic tone in the brain.

“even for the animal studies that used a range of dosages from 0.75 to 1.5 milligrams per kilogram of body weight there is some evidence that in laboratory Miser rats there can be some loss of serotonergic tone in the brains of animals that have been administered MDMA”