Extract from Hallucinogen Pharmacology chapter:

Ergot: Claviceps purpurea (Hypocreaceae) grows as a fungus on grasses, especially rye. The fruiting stalk looks like a purple-black club-shaped growth. The fruiting body feeds on the grass kernels. Ergotism provides the earliest record of mycotoxicosis or poisoning by toxic molds.

Mid-wives passed along the secret to properly dose ergot extracts to aid in childbirth. The ergot extract helped women whose contractions were too weak to expel the baby. Ergot may have been used to induce abortions.

In 1976, Linnda R. Caporael suggested that ergotism caused the bizarre behavior of women in Salem (prompting the Salem witch trials). Subsequent research did not support the proposition.
Extraction of Ergot yields lysergic acid, and this can be purified and chemically converted to LSD. Albert Hoffman first developed the compound in 1938. In 1947, Sandoz Laboratories began marketing LSD for use in psychiatry, claiming efficacy for schizophrenia, sexual perversion, and even criminal behavior.

In the 1950’s and 1960’s, the psychiatrist Humphry Osmond used LSD to treat his patients and reduce their addiction to alcohol. The term "psychedelic" (literally means mind manifesting) comes from Osmond. In 1966, Timothy Leary founded the League for Spiritual Discovery using LSD use as a sacrament.

At 200 micrograms (ug), the mid-range dose of LSD demonstrates a singularly potent molecule. The fit in the receptor is so snug that, besides its low dose, the effects last for up to 12 hours. The drug binds tightly to some of the serotonin receptors and thus can prevent sleep. Other effects include reduced appetite, pupil dilation, and sweating. LSD acts as an agonist to the D2 receptor which may cause some of its psychoactivity. LSD binds to most serotonin receptors, but not to the 5-HT3 and 5-HT4 receptor subtypes. The effects of LSD can be blocked by 5-HT2A antagonists.

Research suggests that LSD increases glutamate release in the cerebral cortex thus excites this region. Another finding shows cross-tolerance between LSD, mescaline, and psilocybin, reinforcing the notion that they all work the same way, at least in part.

The term “microdosing” refers to the practice of consuming low levels of LSD (or psilocybin) to gain stimulation without the high. Producers set the dosages to be 1/10 to 1/20 of the minimum level to hallucinate. In surveys, people microdosing LSD said they did it to enhance performance, to improve their mood or sociability, to obtain relief for physical symptoms, or out of curiosity.