The huge amounts of drug-testing data came from workplaces where urine and other testing was done - so may not be completely representative of all employees.
"American workers are increasingly testing positive for workforce drug use across almost all workforce categories and drug test specimen types," says Dr. Barry Sample, director of science and technology at the diagnostic information company Quest Diagnostics.
Data released by the company show that among about 6.6 million urine drug tests performed in the general US workforce, 4.7% showed positive in 2014 - up on the 4.3% proportion measured in 2013, which itself had seen the first annual rise in figures since 2003.
Dr. Sample comments:
"In the past, we have noted increases in prescription drug positivity rates, but now it seems illicit drug use may be on the rise, according to our data."
Added to the rise in urine-betrayed drug use, oral fluid and hair drug tests showed a rise in illicit workplace activity - the proportion of positives among these 1.1 million tests also increased between 2013 and 2014.
A former director of the US National Institute on Drug Abuse (NIDA), Dr. Robert DuPont says:
"The increases in illicit drug positivity in employment drug testing should get employers and policymakers to take notice of the serious risks these drugs create for productivity, health and safety."
Many of the illicit substances are associated with impaired physical and cognitive function in workers, Dr. DuPont believes.
Quest Diagnostics says it publishes its drug-testing findings as a public service for government, employers, policymakers and the general public, and has done so annually for the past 25 years. The firm provides workplace drugs tests on the behalf of employers.
While the data come from a large sample size and the monitoring is done longitudinally, both of which give strength to the information, analysis is limited by the selection of the testing population. The results are reflective only of workplaces in which employers have drug-testing regimes.
There is a breakdown by drug of choice:
- Marijuana continues to be the most commonly detected illicit drug, with positivity in the general US workforce tested increasing from 2.1% in 2013 to 2.4% in 2014
- On cocaine use, the figures "reverse a prolonged period of decline," with the substance found in 0.22% of urine tests in 2013 but rising to 0.24% in 2014
- Amphetamines: across all specimen types, the positivity rate "is now at its highest level on record."
Dr. Sample comments on the marijuana results, finding the rise "notable" and questioning "if it means that people are more accepting and therefore more likely to use marijuana recreationally or for therapeutic purposes than in the past, even in states where marijuana's use is not clearly sanctioned by state laws. This will be an important area of continued analysis given the national debate about the legality and health impacts of recreational and medicinal marijuana use."
Smoking marijuana daily for 3 years as a teen was linked to having an abnormally shaped hippocampus of the brain and long-term memory problems in a study published in March.