Drugs are detoxified by the smooth endoplasmic reticulum of liver cells (for more about endoplasmic reticulum, see the chapter “Cellular Basics”). Detoxification usually involves changing the molecular structure of a toxin, a modification that increases the toxin’s solubility, allowing it to be safely carried away by the blood and excreted via urine. Cells are able to increase their detoxification efforts when drug levels increase. Investigations conducted with rats that have been injected with a sedative known as phenobarbital have shown a striking increase in the amount of smooth endoplasmic reticulum of the liver cells.