Cocaine brain activity. Coloured positron emission tomography (PET) brain scans of a cocaine user. Front of brain at top, slices get deeper from left to right. Red and yellow areas are those of high activity. The bar at right shows decreasing activity from red to purple. A cocaine user's brain is less active than a healthy brain. Arrows show areas of the frontal lobes where activity is markedly lower. Cocaine is an alkaloid drug obtained from the coca plant (Erythroxylon coca). In a PET scan, radioactively- tagged molecules are injected into the bloodstream and their emissions monitored. Glucose is used here, taken up by active brain cells.