If the test is administered correctly and within a specific time frame after ingesting or consuming a specific drug, it is almost 100 % accurate. Different tests offer different ranges but most report over 99% accuracy. Of course there are ways that the individual being tested can attempt to trick or negate the results of a drug test, which is not a fault of the test. Using an at home drug test that has an adulteration component or test will help ensure that the sample has not been tampered with or the individual has not taken one of the many "cleanse or cleaning" supplements available. Can someone be on drugs but pass an at home drug test? At home drug tests are not comprehensive for every drug that an individual may take. For example, not all prescription drugs will show on at home drug tests, especially if the test administered is only for marijuana and cocaine. Street drugs may also not show if the incorrect test is used. It is essential if parents or professionals are using an at home drug test to have an idea of what drug they should be testing for. Often many parents or even professionals working with children already have an idea of what drugs are likely to be problematic. For people that are working with children or adults that are suspected of drug use, learning the signs and symptoms of various drugs can be extremely helpful. Watching the individual's behavior, physical changes, mental functioning as well as social behavior can really assist in narrowing down the general type of drug that you may want to test for. Can a test give a false positive or a false negative? If the test is administered incorrectly or if the urine, saliva or breath was tampered with in some way then a false negative could occur. In all tests there is a baseline measurement or lower limit of sensitivity to the specific drug. If the at home drug test is given outside of the time that the drug stays at detectable levels in the body then the test will show negative, even though the individual had used that particular drug. Testing within 2 days of most types of suspected use is the best option to avoid this problem. Testing too soon before the body metabolizes the drug can also give a negative reading so that timeframe is important. There are charts provided within at home drug test kits to help testers know the timeframes to watch. False positives can rarely occur however generally it is because the child or individual is on some type of prescribed medication that cannot be distinguished from a drug you are testing for. Many ADHD medications will show as amphetamines and many anti-depressants will often show as benzodiazepine positive. If your child or the adult you are testing is on a prescription for these groups or types of drugs, consult with your doctor before using an at home drug test.