Is it possible to make a clean urine sample fail by putting a drug into the sample after its been collected?

Question

For example, You take a drug test & then afterwards someone sprinkles a small amount of a drug (cocaine, crushed pill, etc.) into your sample without you knowing about it.

Don't get me wrong, I'm sure it'll detect the drug but I was wondering if the test has a way to flag whether the drug was metabolized through your system or not. Also, being that the trace amounts of a drug in your urine are so very small I'd think that the test results would be able to tell that something wasn't right.

Answer 1

No. The sample is sealed in front of you and you sign the seal. Most drug tests are for both the drug and the metabolites.

Answer 2

It depends on what the drug is and how the test is done. A drug undergoes chemical changes in the body as it is processed, and advanced laboratory methods can detect both the original drug and the substances that are produced when the body processes the drug (aka the drug's metabolites). More simple lab methods only detect a limited range of substances. For certain drugs, even the simple lab methods look for a drug metabolite. Examples are heroin (but not other opiates), methadone, cocaine and possibly nicotine - so the simple test will only give a positive if these drugs have been through the body. For most other drugs, you could add the stuff afterwards and get a positive result with a simple test. However, any drug result that is going to be used for legal purposes (e.g. to convict someone of a crime, to determine the cause of a death, to ban someone from a sport) will be analysed with the most advanced methods available. For these samples there must also be a "chain of custody", i.e. there is a record of everyone who has handled the sample and who has access to the place where it is stored.