Drug testing can be a controversial topic. It's a subject that is loaded with all kinds of judgements based on personal perspectives on both legal and illegal recreational drugs.
Hopefully we can answer some of your questions here. This page isn't meant to be the final word on the subject, it's intended to be a resource for people who want to use a drug screening test for what ever reason.
If you have questions about addiction The New Zealand Drug Foundation is a great resource.
How do drug tests work?
The drug tests you are most likely to have seen on TV where someone pees in a cup or has a swab taken of their mouth are immunoassays (IA). Immunoassays are a clever bit of biotechnology. In short an antibody is made that binds specifically to the drug you want to detect. When the anibody binds to the target drug a colour change occurs. The most common type of this kind of test is the pregnancy test.
How accurate are home drug tests?
This depends on the quality of the test, and what you are testing for. The big thing to remember here is that IA test are only a screening tool. Some drug test are susceptible to interference from other compunds (like prescription medicines, over the counter medicines, and some foods). Manafacturers of drug tests usually supply lists of potential cross reacting substances with their tests.
That being said test can usually detect the target substance to the level of 50 nanogrammes per millilitre. Which is a really small amount, 0.00000005g in 1mL of liquid to be a bit more precise.
How quickly do home drug tests work?
Taking the sample, swabbing the inside of your mouth take about 1 minute. The test reaction itself takes about five minutes. It's important to check the instructions of the particular test you use to make sure you do the process correctly. The most important thing to get right is the read time. Most IAs can't be relyed upon after about 15 minutes from the sample being applied to the test (in other words 15 minutes from dipping in the test urine, or finishing the mouth swabbing)
What can the tests detect?
IA tests can be made to detect a wide range of things from pregnancy hormones, to THC the active in Marijuana, to P (Methamphetamine) and so on. It's important to check *before you buy the test* what it will test for.
Does a positive test mean addiction?
Short answer no. Addiction is a complex medical problem. There are some people who use recreational drugs regularly who aren't addicts, there are some people who use them a few times and become addicted. It depends on the person and the drug they are using. Ecstacy and P (MDMA and Methamphetamine) are both amphetamine based drugs. MDMA is less risky in terms of addiction and risk of harmful outcomes than P. The risk of addiction with P is all about it's chemistry.
Do I have to get consent to test someone else?
Yes. If you want to test your kids it's a good idea to talk to them about it first. The answer you get from them will probably tell your more than the test.
Can home test results be used against me by employers or the police?
My understanding is no, they cannot. IA test kits are a screening tool only. To the best of my knowledge to have any legal standing positive reulst must come from a certificated laboratory, using specialised testing equipment.