The lethal dose of LSD (LD50) has never been determined; however, it is estimated to be about 70,000 times the minimum dose, and there have been cases of heart attacks and strokes associated with LSD use but it's unclear if the drug was the direct cause.
Research with classic psychedelics has shown a connection between the depth of a mystical experience and therapeutic outcomes for addiction, life-threatening illnesses, and OCD. While participants in low-dose MDMA therapy did still experience improvements, those who received an inactive placebo did even better.
The challenge with dosing for psychedelics is that there isn’t any consistency between products, but methods can include volumetric measuring of a fully dissolved solution for accurate dosing. This is an important practice as many people mistakenly take doses that are too large, instead of “microdosing” as intended.
James Fadiman explains that microdosing is a sub perceptual amount of psychedelic taken on a frequent basis, which is believed to provide several benefits without the full psychedelic experience. However, studies have shown that microdosing can cause anxiety in some people.
MDMA can cause long-term damage to the serotonin system with a certain dose and frequency, while classic psychedelics have a higher level of physical safety. Nonetheless, MDMA is within the subset of classic psychedelics in terms of its subjective effects.