This page looks at different types of drug tests, how they are carried out and some of the things that might affect their results. On this page we cover:
- What is a drug test?
- What are the limitations of drug tests?
- What can affect how long a drug stays in my body?
- What are the differences between different types of drug tests?
- How can I pass a drug test?
- Will drinking lots of water give me clean urine faster?
- What if I take more than one drug?
- What is a false positive?
- Can I test positive from inhaling someone else's cannabis smoke?
- Why does cannabis stay in the body for so long?
- Do home drug testing kits work?
- Pub and home breathalysers
- Can people be forced to have a drug test?
What is a drug test?
Drug testing looks for traces of drugs in the body using samples of urine, breath, hair, saliva, or sweat.
Drug tests detect whether you are under the influence of alcohol or whether you have taken drugs recently. Drug tests use samples to look for very small amounts of drugs in the body. There are different types of drug tests, including breath, blood, hair, saliva and urine, which test for various drugs.
Testing may be used by a range of organisations including:
- Workplaces to check for past use of illicit drugs and blood alcohol concentration while working.
- Sporting bodies to detect drugs that are not permitted while competing in certain competitions.
- Drug treatment services to inform medical decisions.
- Judicial settings to inform legal decisions such as in custody cases.
What are the limitations of drug tests?
Drug tests can't tell exactly how much of a drug was used or exactly when it was used. Drug tests also don’t measure impairment, apart from alcohol breath testing.
Laboratory testing is necessary to confirm any positive test to and is generally more accurate than ‘point-of-collection testing’ (POCT), but it’s not always exact. POCT devices provide more timely results, but laboratory analysis can better differentiate illicit from prescription drug use.
What can affect how long a drug stays in my body?
Drugs affect people differently, and are metabolised (processed) by people differently. Results of drug tests are always unique to the person who was tested. This means that you and a friend could take the same amount of a drug, at the same time, and have the same type of drug test, but have different test results. This is because individual things about you and your drug use can affect the results.
- the strength of the drug
- how much of it you use
- how you use it (e.g. drunk, smoked, injected)
- how often you use it
- what other drugs you use
- tolerance to the drug
- gender and age
- overall health and wellbeing
What are the differences between different types of drug tests?
What they test for: Alcohol
Method/process: Blow into a hand held device.
Used by: Police, workplaces. Random roadside breath testing for alcohol takes place in New Zealand.
Detection time after last use: It takes approximately 1 hour for the body to break down each standard drink.
What they test for: Can test for all prescription and illicit drugs, including some forms of synthetic cannabis. Tests can be modified to detect particular substances.
Method/process: Urinate into a container. The urine will be tested using a dipstick. If the test is positive the urine sample will be sent to a laboratory for more testing.
Used by: Workplaces, drug treatment centres, sporting bodies.
Detection time after last use: Cannabis up to 10 days (infrequent use) or 30 days or longer (frequent use), opiates 2 to 4 days, amphetamines 2 to 5 days, cocaine 2 to 3 days, benzodiazepines up to 2 weeks.
What they test for: Can test for all illicit and prescription drugs. Tests can be modified to detect particular substances. Sometimes used instead of or to confirm a breath test for alcohol.
Method/process: A blood sample will be taken from a finger prick, or from a vein in the arm or hand, using a needle. The blood sample will be tested by a laboratory.
Used by: Police, drug treatment centres, sporting bodies.
Detection time after last use: Cannabis 20 to 36 hours, amphetamines 4 to 8 hours, cocaine 40 to 90 minutes.
What they test for: Can test for use of cannabis, amphetamines, MDMA (ecstasy), cocaine, opiates and some benzodiazepines.
Method/process: An absorbent collector is put in the mouth or on the tongue.
Used by: Workplace.
Detection time after last use: Cannabis 3 to 4 hours, amphetamines 12 to 24 hours, cocaine 4 hours and possibly longer, MDMA (ecstasy) 12 to 24 hours. Detection times for opiates and benzodiazepines are currently unknown.
What they test for: Can test for all illicit drug use and some prescription drugs.
Method/process: Approximately 40 to 50 strands of hair will be cut from the scalp line at the crown of the head. The hair sample will be tested by a laboratory.
Used by: Sporting bodies, justice settings.
Detection time after last use: Can detect past use up to a few months, and can therefore test for chronic use. Hair drug tests are currently the only tests that can reliably detect drug use beyond a couple of days or weeks. However, hair tests are not used very often because they are expensive.
How can I pass a drug test?
Other than not taking drugs, the only sure way to pass a drug test (i.e. to test negative) is to make sure your body has metabolised (processed) all of the drug(s) you have taken.
Getting a negative drug test result (i.e. passing) means:
- that you haven't taken the drug(s) being tested, or
- that your body has metabolised all traces of the drug(s) being tested, or
- that the test wasn't complex enough to find the traces of the drug(s) being tested.
There are myths that taking various substances (e.g. aspirin, niacin, bleach, vinegar, cranberry juice, goldenseal) will mask or disguise drug use in tests and give you a negative test result. There are also products sold that claim they can help you pass a drug test. However, there's no reliable evidence that any of these actually work.
It is not possible to 'cheat' a hair test except by using someone else’s hair. Bleaching and dying hair do not compromise the testing.
There's no guaranteed way to get rid of a drug other than waiting for your body to metabolise it. If you know you will be drug tested and you are worried, don't use drugs. Help and support is available.
Will drinking lots of water give me clean urine faster?
Drinking lots of water does not work to cheat a urine (or a blood) drug test. Most urine tests check for dilution (too much water) and may reject your results because of this.
Also, you can actually get sick from drinking more water than your body can handle. This is called "water intoxication" or "water overdose". If you drink too much water, your kidneys can't get rid of it quickly enough. This can cause headaches, blurred vision, cramps and eventually convulsions.
What if I take more than one drug?
If you have taken more than one drug at a time (including alcohol), your body may take longer to metabolise them than if you had only taken one. Most drugs will stay in your body for at least 24–48 hours, so they don't need to be taken at exactly the same time to have an effect on each other.
Remember that even if you don't feel the effects of the drugs anymore (e.g. you don't feel stoned), they can still be in your body.
What is a false positive?
A false positive is a test result that is positive for a drug that you haven't taken. It is false because the result is incorrect. A false positive usually means that the test wasn't sensitive enough to be able to tell the difference between two drugs.
Can I test positive from inhaling someone else's cannabis smoke?
Traces of cannabis could be found in your body fluids if you have inhaled someone else's cannabis smoke (called passive cannabis smoking). However, testing companies usually say that the concentrations of these traces would be too low to give a positive test result for cannabis.
Why does cannabis stay in the body for so long?
Cannabis is stored in the body differently to other drugs. If you use cannabis once, the body can get rid of it fairly quickly (within a couple of hours). However if you are a regular user of cannabis, the THC (the active ingredient in cannabis) accumulates in your body's fat cells and can take a long time to be broken down and metabolised. THC can be detected by a urine test for up to 6 weeks after regular use.
Do home drug testing kits work?
Drug testing kits can be bought over the Internet. There are different types of kits, which test a range of drugs. These kits are often promoted to parents as a way of finding out if their kids have used drugs. However, there's little evidence that these kits are accurate or reliable. Also, there can be issues with actually doing the tests. For example, if a parent wanted to test their kid, who didn't want to be tested and denied taking drugs, their relationship could be seriously affected.
There are also kits available for sale that are designed to test the strength, purity and make-up of drugs. But again, there has only been only a small amount of research into how accurate and reliable these tests are, so be wary of any claims made by the test manufacturers or sellers.
Pub and home breathalysers
Many pubs and bars have breathalysers available for patrons to use. There are also a number of personal breathalysers available for purchase, for example at petrol stations. These breathalysers should only be used as a general guide of BAC levels. They are not recommended for calculating if a person can drive or not and test results cannot be used in a court of law or to question a result obtained through a police breathalyser.
Can I be forced to have a drug test?
At some point in your life you may be asked to have a drug test.
New Zealand’s public schools don't routinely drug test their students. Drug tests are sometimes required where a student has been suspended and the school Board of Trustees requires that the student agree to drug testing as a condition for reinstatement to school. In contrast, drug testing of students in private and boarding schools may be part of the school's drug policy. If you are a student in one of these schools, you could be asked to have a drug test.
Drug testing in workplaces is usually used when there are safety issues related to the job, such as driving a vehicle or operating machinery. If you are employed in this type of work, you could be asked to have a drug test as a requirement of the job. There will probably be consequences if you refuse, such as losing your job.
If you are driving a motor vehicle in New Zealand, and refuse a random roadside breath test (for alcohol) when you are asked to have one, you can be fined or lose your licence. At this stage, roadside saliva testing for other drug use is not used in New Zealand.
Disclaimer Information on this page is meant as a general guide only. While we (the New Zealand Drug Foundation) have worked hard to make sure that the information on this page is complete and correct, we do not claim that it is perfectly complete, accurate, reliable or suitable. We do not offer any information in this fact sheet as a tool for treatment or counselling. We recommend that before making any decision based on any information in this fact sheet, you should seek independent professional advice.
This information on this page was adapted from the Australian Drug Foundation’s ‘DrugInfo’ site.