Could more use of medical marijuana help increase the supply of older workers?

Maybe so. But that matter is clouded by more than a haze of blue smoke.

Here's what you need to know.

Passage of medical marijuana laws "leads to increases in labor supply among older adults along with improvement in health for older men," according to a new study from the National Bureau of Economic Research.

The authors came to that conclusion after studying health and retirement data in annual reports from 1992 through 2012, which they published in a paper titled, The Impact of Medical Marijuana Laws on the Labor Supply and Health of Older Adults: Evidence from the Health and Retirement Study

"We provide evidence that there may be benefits in terms of pain reduction and labor supply of older adults," states the report by Lauren Hersch Nicholas and Johanna Catherine Maclean, at Johns Hopkins School of Public Health and Temple University, respectively.

For sure, it's increasingly common for hiring managers to complain about lack of skilled and experienced workers, so more labor supply would be welcome. And of course, any person with even a modicum of humanity wants to reduce pain and suffering due to health issues.

If this study helps medical marijuana get a legal nod in every state, that would be great for stocks in the North American Marijuana Index. The index is already beating the stocks in the SPDR S&P 500 (SPY) exchange-traded fund hands down so far this year.

Pipe dreams?

Unfortunately for pot investors, the idea that in short order, every sick senior will light up may be little more than a pipe dream. The problem is that marijuana isn't the same as alcohol.

"With alcohol, not only is it easy to test for impairment, but there are consensus levels of what constitutes impairment both in the scientific community and the legal system," says Dr. Barry Sample, senior director of science and technology at Quest Diagnostics  (DGX) employer solutions, which is perhaps best known for conducting employee and pre-employment drug tests.

By impairment, Dr. Sample means the effect the drug has on a person's ability to do his or her job or operate a car, for instance. 

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