Cocaine detoxification. Coloured positron emission tomography (PET) scans of horizontal sections of a normal brain (top) and a brain four months after heavy cocaine use. The front of the brains are at top, and the slices get deeper from left to right. The brighter (yellow) areas of the brain are those of high activity. The brain of the cocaine user is seen to be less active than the healthy brain, even after four months of abstinence. Cocaine is an alkaloid drug obtained from the coca plant (Erythroxylon coca). In PET scans, radioactively- tagged molecules are injected into the bloodstream and their emissions monitored. Glucose is used here, as it is taken up by active brain cells.