Rationale for urine testing flawed – study finds marijuana use lowers accident risk

Testing urine for cannabis does not improve on-the-job safety. It not only fails to measure impairment, a new study confirms cannabis users have an even lower accident risk than straight people.

The entire reasoning for drug testing workers and drivers is based on the assumption that any use will cause impairment and therefore users would endanger themselves and others around them. Now a new study has undermined the rationale for drug testing workers, by showing that the use of cannabis actually reduced the risk of accidents.

Investigators at the Luasanne University Hospital in Switzerland assessed the association between the use of cannabis and/or alcohol and the risk of injury among 486 patients aged 16 and older treated for various injuries. They found alcohol use in the six hours prior to injury was associated with a three-fold elevated relative risk compared with no alcohol use, but cannabis use was inversely related to risk of injury, with only 0.33 the risk compared to no use. Cannabis users had less injuries and were actually safer than alcohol drinkers or even straight people. Despite the study’s relatively small sample size, investigators concluded:

“The results for cannabis use were quite surprising. … The present study in fact indicated a ‘protective effect’ of cannabis use in a doseresponse relationship.”

A prior case-control study conducted by the University of Missouri also reported an inverse relationship between marijuana use and injury risk, finding, “Self-reported marijuana use in the previous seven days was associated … with a substantially decreased risk of injury.”

Drug testing in New Zealand

Employers often say they have to drug test workers because of the Health and Safety in Employment Act 1992, but they must also take into account the Privacy Act 1993, the New Zealand
Bill of Rights Act 1990 and the Human Rights Act 1993.

Under New Zealand employment case law, testing is allowed for:

• Pre-employment
• Post accident/incident
• Just ‘cause’
• Follow-up (after a positive test)
• Random or periodic testing for safety-sensitive positions.

New Zealand and Australia follow a common standard for urine tests (AS/NZS 4308:2008), which is based on the US Standard. It permits only two methods for analysing urine: EMIT or GCMS. No other type of urine test, and no other type of test such as hair, saliva or sweat, meets the standard because they are unreliable and have a high rate of incorrect positives and negatives.

Only EMIT and GCMS urine tests can be used for evidential purposes, and any other type of test should be challenged.

  • EMIT tests are usually conducted at doctor’s surgeries or medical centres or places like MedLab.
  • GCMS tests are performed by the government-owned ESR, who have close ties with the police and who also analyse samples collected by NZ Drug Detection Agency Ltd, a privately-owned testing outfit run by former cops.
  • A simple on-site “screen” is sometimes used (that often resembles a home pregnancy kit) but these do not meet the standard and must be confirmed with proper lab analysis.

Urine tests are made to detect only the presence of THC-COOH, the non-psychoactive metabolite
of THC. A cut-off of 50ng/ml is allowed, supposedly to allow for any second hand smoke, but that figure is actually fairly arbitrary and based on little real science.

Evidence-based testing

Drug testing advocates claim it is about safety, but they only look for the inactive metabolite that remains after someone straightens up. THC from marijuana is converted to THC-COOH, which is fat soluble and can stay in the body for several months after use. Because urine analysis does not measure the presence of THC it cannot indicate when cannabis was inhaled or ingested, or whether a person is impaired.

If testing really was about on-the-job safety, as they claim, testers could just as easily look for the presence of THC itself, which is present while a person is high. Testers could set a limit for THC based on actual impairment.

In 2007 a research team led by Franjo Grotenhermen at from the Nova Institute in Germany showed a THC level in blood of 10ng/ml was equivalent to the legal drink-driving limit of 0.05. The study found that a level below this was not associated with an increased risk of injury.

Setting an THC level that is based on evidence and comparable to alcohol impairment would be more effective, just, and more widely accepted by workers and smokers.

Beating the test

The biggest question on the lips of most pot smokers is how long they have to stop in order to give a clean urine test. In anecdotal reports people say it takes anything from 2 days to 6 weeks to be clean, but there has not been a lot of actual research on the subject.

In a new study by the US National Institute on Drug Abuse in Maryland, USA, 60 regular cannabis users were monitored during 30 days of abstinence. Their urine was tested for the presence of THC-COOH, the non-psychoactive metabolite of THC. Surprisingly, researchers found there were considerable fluctuations between days with a positive urine test and days with a negative test during this period, rather than a constant decline in THC-COOH concentrations. The average number of days until the first negative test (THC-COOH below 50 ng/ml) was 3.2 days, while the average number of days until the last positive test was 15.4 days.

If you can’t wait that long, many stores now sell products designed to beat urine tests and maintain your privacy. But just as there are two officially sanctioned types of urine test, and others that are not approved, there are specialised products designed to work for each one. Make sure you get the right product for the test you are taking, or it may not work. One of the most widely used products is synthetic urine, that comes with a heating pad and pouring spout. It’s unisex, completely undetectable, and beats all types of urine test.

Sources: Goodwin RS, et al. J Anl Toxicol 2008;32(8):562-9; Gmel G, et al. BMC Public Health 2009;9(1):40. Grotenhermen, F., et al, (2007), Developing limits for driving under cannabis. Addiction, 102: 1910–1917. doi: 10.1111/j.1360-0443.2007.02009.xVinson DC, Marijuana and other illicit drug use and the risk of injury: A case-control study. Missouri Medicine [2006, 103(2):152-156]

Declaration of interest: the author is the manager of The Hempstore.

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