A growing number of genetic tests could help avoid some of the 700,000 serious drug reactions in the United States each year, according to some experts. These tests, which are controversial, can help determine how people are likely to respond to common medications by looking for tiny variations in genes that determine how fast or slow a person metabolizes medications. Some drugs can result in life-threatening emergencies, and many have widely varying effects. FDA includes cautionary information for people with certain gene variations on the labels of more than 100 prescription medications, but only 20% of doctors order the tests. This is because the lack of large, randomized trials has prevented some medical associations from endorsing the tests. They are also expensive, ranging from $500 to as much as $2,000. About 75% of prescription and OTC drugs depend on a few liver enzymes to be absorbed, and 95% of people have at least one minor variation in the genes that regulate these enzymes. This can cause someone to be a "poor metabolizer," or someone with a higher risk of a toxic reaction to a drug. Many hospitals are now including information in patient records so that doctors can choose the most useful drugs and dosages for patients in the future.