LSD

Lysergic Acid Diethyamide

Lysergic Acid is an Ergot Alkaloid.

Ergot Alkaloids can be used medicinally, despite the fact that some of them are v.toxic and poisonous.

They are toxic, as they are thought to be responsible for Ergot disease.

Ergot disease is a fungal disease of plants.

The fungi species Claviceps is responsible for this plant disease.

During this disease, plant (usually rye) grains become harder and seedlike ("ergots").

If humans and animals consume the diseased grains, they get poisoned.

As for LSD:

"LSD is sold on the street in tablets, capsules, and occasionally in liquid form. It is an odorless and colorless substance with a slightly bitter taste that is usually ingested orally. It is often added to absorbent paper, such as blotter paper, and divided into small decorated squares, with each square representing one dose.

The short-term effects of LSD are unpredictable. They depend on the amount of the drug taken; the user's personality, mood, and expectations; and the surroundings in which the drug is used. Usually, the user feels the first effects of the drug within 30 to 90 minutes of ingestion. These experiences last for extended periods of time and typically begin to clear after about 12 hours. The physical effects include dilated pupils, higher body temperature, increased heart rate and blood pressure, sweating, loss of appetite, sleeplessness, dry mouth, and tremors. Sensations may seem to "cross over" for the user, giving the feeling of hearing colors and seeing sounds. If taken in a large enough dose, the drug produces delusions and visual hallucinations.

LSD users often have flashbacks, during which certain aspects of their LSD experience recur even though they have stopped taking the drug. In addition, LSD users may develop long-lasting psychoses, such as schizophrenia or severe depression. LSD is not considered an addictive drug - that is, it does not produce compulsive drug-seeking behavior as cocaine, heroin, and methamphetamine do. However, LSD users may develop tolerance to the drug, meaning that they must consume progressively larger doses of the drug in order to continue to experience the hallucinogenic effects that they seek."

http://www.usdoj.gov/dea/concern/lsd.html