Lysergide (LSD) is a semi-synthetic hallucinogen, and is one of the most potent drugs known. Recreational use became popular between the 1960s to 1980s, but is now less common. It is generally believed that most LSD is produced outside Europe, but secondary preparation of dosage units by dipping or spotting paper squares is more widespread. These dosage units usually bear colored designs featuring cartoon characters, geometric and abstract motifs. LSD is related to other substituted tryptamines, and is under international control.

Because LSD is so potent, there is no need for it to be adulterated. Laboratories rarely encounter the drug as a powder so rarely measure purity. As mentioned earlier, the drug decomposes in light and at high temperatures.

LSD is taken orally. Paper doses are placed on the tongue, where the drug is rapidly absorbed. Tablets or capsules are swallowed. LSD is not absorbed through dry skin.

Medical use
Although once used in psychotherapy, LSD has no current medical use.