How drug tests work

As drug testing becomes increasingly common, looks at what the tests can pick up.

drug test form

"Do I need to pee on this?"

How do drugs test work?

Your body attempts to break down anything you shove inside it, from food to drink and drugs. ‘Metabolites’ are formed as part of this process, and testing looks for specific types that could only occur as a result of drug taking and which can remain inside the body for long periods.

How long does it take for a drug to not show up on a test?

If a tester had to nominate the most easily detectable drug, it would probably be cannabis. The active ingredient in cannabis is called THC, and the metabolites from THC can take up to 45 days to clear the body, depending on your body size and drug habit. As a non water-soluble substance, you can’t flush THC from your system overnight. Instead, it tends to get caught up in the body and released at a much slower rate.

Here’s a rough guide to some other drug metabolites that outstay their welcome, and which a urine test won’t miss:

Drug tests on hair

Drug metabolites can be also be detected in blood, perspiration and other body residue, but hair is an increasingly popular testing ground. Why? Because metabolites can supposedly filter out with hair growth and resist pretty much everything from shampooing to perm jobs. Testing involves dissolving the hair sample in a series of solvents that extract the drug metabolites. Many people think these tests could be unreliable.

Can you dodge a drugs test?

Short of shaving your head, or having a ready supply of infant wee to hand, there is no sure-fire means. There are many products on the market that claim to beat the test, mostly by adding masking substances to your urine sample. However, the means of detection is becoming increasingly sophisticated, so what might work one day might fail badly the next.

But I’m innocent!

Drug testing is effectively in its infancy. At present, it is believed that more than 250 over-the-counter medicines, and some food ingredients, could cause a false positive result. So expect many legal disputes as the practice becomes more widespread in the workplace.

Drug testing on arrest

If you’re arrested for a ‘trigger offence’, you may be tested to find out if you’ve taken any Class A drugs. Trigger offences include: theft, robbery, burglary, motor vehicle-theft, handling stolen goods, possession of an illegal drug and possession of an illegal drug with intent to supply.

A person cannot be forced to provide a sample for testing, but it is an offence to refuse to provide a sample without good cause.

If you test positive for Class A drugs, you’ll be required to attend a compulsory drug assessment by specialist drugs workers. The assessment will determine the extent of your drug problem and help you into treatment and other support, even if you’re not charged with an offence.

Those who fail to provide a sample or comply with a required assessment face a fine of up to £2,500 and/or up to three months in prison.

Photo of drugs test by Shutterstock

Next Steps

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Updated on 29-Sep-2015