This is potentially bad news for the legal marijuana movement

The Motley Fool – by Sean Williams

There are few issues as polarizing as whether or not marijuana should be legalized on a recreational or medical level. Yet in spite of the wide variance in views, marijuana’s recent momentum towards legalization is undeniable.

Marijuana gains momentum
Since 1996, when California became the first state to legalize the use of marijuana for medical purposes, we’ve witnessed 22 additional states pass laws allowing for its medical use. Furthermore, in 2012 and 2014 we saw a pair of states pass laws allowing for the legal sale of recreational, adult-use marijuana. In fact, one of the biggest victories for marijuana proponents came this year when residents in Alaska and Oregon both voted to legalize recreational marijuana.  

Although estimates vary wildly, no one would argue with the assumption that a sweeping legalization of marijuana, or the continued legalization of marijuana on a state-by-state basis, will result in substantial tax revenue for legal states. Greenwave Advisors suggested in a recently released report that a sweeping legalization would swell marijuana’s market value to $35 billion by 2020, while the path we’re on now would still boost its value to $21 billion by 2020. Also, NerdWallet estimated in September that U.S. states could net $3.1 billion in new tax revenue if marijuana were legalized across the board.

Marijuana’s two big obstacles
But there are two major obstacles that continue to weigh on marijuana’s growth.

First, it remains an illegal (schedule 1) drug according to the federal government. This classification denotes that marijuana has no medical benefits whatsoever, which isn’t good news for proponents and patients hoping to see marijuana’s indications expanded in the medical field.

The second growth constraint feeds off the first point: there just aren’t many long-term studiesthat examine marijuana’s effects on the body. Less than one-tenth of all marijuana studies have been geared toward its benefits, and many of these studies only began emerging within the past few years as marijuana’s approval momentum gained steam. It’s going to take some time before we have conclusive data in either direction that marijuana is safe or not.

A recent study, however, would suggest marijuana’s safety is potentially taking a step back rather than forward.

Marijuana safety potentially takes a step back
Based on an abstract received by the Proceedings of the National Academy of Sciences in August, marijuana may have adverse effects on brain development over the long term in adolescents.

The study in question pitted 48 marijuana users between ages 14 and 30 (average age of 18) against 62 nonusers as the control group to measure various aspects of cognitive function over time. The testing involved an MRI scan for each individual, regular urine analysis, and an IQ test.

The results showed that marijuana users had an average IQ that was five points lower than the control group. In addition, MRIs showed that regular marijuana users had less gray matter in the orbitofrontal cortex, a region of the brain responsible for decision making and motivation. The concern here being that young minds are easily shaped while still maturing, so excessive use of marijuana during adolescence could have negative long-term cognitive implications.

But I’d be remiss if I didn’t mention that the study wasn’t conclusive. One of the study’s authors, Francesca Filbey, commented, “While our study does not conclusively address whether any or all of the brain changes are a direct consequence of marijuana use, these effects do suggest that these changes are related to age or onset and duration of use.”

The real damage done
Though the study wasn’t conclusive, it does serve to increase the cloud of uncertainty surrounding marijuana. As long as conflicting studies continue to emerge, it makes the possibility of the federal government changing its tune on the drug increasingly slim.

Studies like this also remain a concern for cannabinoid drug producers, which are looking to develop medicines utilizing chemicals found in cannabis plants. None is likely more well-known than GW Pharmaceuticals (NASDAQ:GWPH  ) , which has discovered in excess of five dozen cannabinoids and is developing a handful of clinical-stage therapies to fight cancer pain and adult and pediatric epilepsy, and could even treat type 2 diabetes. Data from GW Pharmaceuticals in its early stage studies has looked promising, and further underlines the potential of cannabinoids for medical purposes.

Uncertainty surrounding marijuana’s long-term usage could stymie the sales potential of cannabinoid-based drugs like those being developed by GW Pharmaceuticals, and could certainly dissuade new participants from attempting to develop cannabinoid-based medications.

The battle continues but the solution remains the same
Going forward, the battle between marijuana’s benefits and its risks will continue to be waged until we have enough long-term evidence to make an educated conclusion about its proper medical use.

Speaking personally, I’d suggest that momentum still swings toward ongoing medical legalization of the drug, considering that cancer patients and those suffering from chronic pain have experienced benefits from medical marijuana for years, if not more than a decade. Further, recent abstracts demonstrating the possibility that marijuana could improve the lives of type 2 diabetics and people with brain cancer give me reason to believe we’re going to see a surge in studies exploring the benefits of marijuana in the coming years.

However, I do remain extremely skeptical of marijuana stocks in general. Emotions surrounding marijuana are heightened, and that often means logic isn’t coming into play as much as it should. GW Pharmaceuticals, for example, is valued at $1.4 billion despite only having one approved therapy in overseas markets (Sativex) which, frankly, isn’t selling very well. Until their long-term benefits are well established, marijuana stocks will remain a very risky proposition.