Lysergic acid diethylamide or LSD is an illegal drug classified as a psychedelic hallucinogen, which was first synthesised by a Swiss researcher, Albert Hoffmann in 1938 - although it's powerful effects were not known until 1943. Though synthetic, LSD is derived from the ergot fungus which grows on grain. It is generally used recreationally for its hallucinogenic effects, which can include synethesia or the perception of one sensation through another sense, such as "seeing music"; as well as altered visual perception - such as objects warping and changing colors. Contrary to popular belief it is very uncommon for users to actually hallucinate something which does not exist - rather the drug usually warps and alters perception of real things. The drug also has powerful effects on a person's ability to make decisions. Several members of the counterculture movement of the 1960s gave great credit to the drug in improving their own creativity, such as the academic Timothy Leary and the cartoonist Robert Crumb.
However, LSD does have a number of side effects, which vary widely from person to person, but are generally minor compared to its powerful effect on the mind. Tachycardia, arrhythmia, minor insomnia, sweating, and tremors are often reported. In addition, the hallucinogenic effect of the drug is not always pleasant, leading to the proverbial "bad trip" - usually described as a strong sensation of terror, paranoia, dysphoria and panic. The tendency to have a negative hallucinogenic experience is greatly dependant on the setting the user is in, and their mindset during the experience, but there is no way to control the experience completely. An LSD "trip" usually lasts from 8 – 12 hours.
LSD does not cause mental illness in healthy people. However, using LSD can sometimes bring on mental illness early in people who were predisposed to them (i.e.: they would have developed mental illness at some point anyway), and will generally make the symptoms of psychosis worse in people who already have a mental illness such as schizophrenia.
It should be noted that although LSD is derived from ergot, it is not the cause of ergot poisoning, and unlike ergot itself - LSD is not very physically dangerous. LSD has never been shown to cause physical addiction, and habitual use of the drug is difficult because tolerance builds up extremely quickly. A user looking to take LSD two days in a row might have to take 2-3 times the normal dose for the same effect, with each continual day of use increasing the needed dose exponentially. Tolerance normally resets completely between 1 – 2 weeks from the last dose.
LSD is incredibly potent. Doses are typically measured in micrograms (thousandths of a milligram). Whilst "overdosing" on LSD is possible in the sense that a user accidentally take more than they wished to; it should be noted that there has never been a recorded death from LSD. The dose of LSD required to kill a human is not known, but it is hypothesised to be well over 10,000 normal doses.
In Distractions, House doses himself with LSD to relieve a migraine headache, and then takes antidepressants to deal with the effects of the LSD. Although several physicians have proposed several therapeutic uses of LSD, it is currently a totally restricted drug in most countries and may not be used or possessed legally for any purpose without a special license from the government, very few (if any) of which are issued.