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Why don’t more doctors prescribe cannabis to their patients?

August 2, 2018

Even as support for medicinal cannabis gathers momentum among voters, physicians often remain hesitant or firmly opposed to recommending cannabis to their patients. Mostly, their hesitation stems from a lack of supportive data and strong clinical trials. But when it comes to cannabis, is the science really not sufficient to support its clinical use?

To better understand why many doctors hesitate to embrace cannabis, let’s consider the factors that have plagued the pro-cannabis argument:

  • First, a lack of available scientific studies on many health outcomes leaves us with mostly anecdotal reports of its medicinal abilities. While these stories certainly have value in guiding scientific investigation, they’re ripe with bias and a spectrum of confounding factors, so they’re not sufficient on their own.
  • Next, when results suggest that cannabis is ineffective at treating a condition, or may have small benefits but substantial side effects, it’s hard to support using cannabis for that clinical condition.
  • Lastly, inconsistency in cannabis’ effects across published reports reduces confidence in the predictable and consistent therapeutic benefits of cannabis.

Let’s break these points down.

Why are there few scientific studies into cannabis’ clinical benefits?

The reason for the relative scarcity in clinical cannabis studies stems largely from its Schedule I classification by the Drug Enforcement Agency. This classification regulates how cannabis can be studied, the access scientists have to cannabis, and the financial and institutional resources that can be devoted to studying cannabis.

You won’t be surprised that it’s especially challenging to acquire funding to study a drug with “currently no accepted medicinal use,” according to the definition associated with its classification. It doesn’t matter that the same drug is one of the earliest known medicines. Most scientists’ careers live and die by grant funding, and the United States government is the single largest source of science funding in the world.

So if the government is resistant to funding medicinal cannabis research, it has a major impact. (And when they do commit to funding, not everyone is happy about it. For instance, Professor Michael Morgan of Washington State University in Vancouver received funding to study the interaction between THC and morphine on pain. This research was listed in Tom Coburn’s (R-OK) list of the top 100 Wasteful Stimulus Projects).

Is the research truly not available?

It turns out, there’s a trove of clinical research studies that the public doesn’t see. Because of the federal restrictions on research in academic institutions, private companies have taken it upon themselves to gather their own data, often with the support of nurses or physicians. The data gathered are being used to optimize the therapeutic effectiveness of their own products and are revealing, so we’re told, exciting and promising results.

Because these companies aren’t gaining approval through the same institutional review boards that are required for academic institutions, they’re often precluded from publishing in the peer-reviewed journals that are publicly available. Another downside is that they don’t receive the same scrutiny for the validity of their results.

Nonetheless, this privately collected trove of clinical data likely represents a significant source of clinical cannabis studies that could be used to transform the industry. But for now, few are showing their hands.

Why is the effectiveness of cannabis inconsistent across studies?

Beyond the challenge of acquiring research funding, it’s not easy—or in many cases possible—to get cannabis for clinical trials that’s consistent with what’s available to consumers.

The inability to systematically test different strains and products has traditionally led to an inability for the clinical research to support many claims by cannabis patients.

For decades, the University of Mississippi has been the only licensed facility to produce the plant for research purposes. But some researchers claim that the cannabis they receive doesn’t resemble the appearance or smell of traditional cannabis, it may be moldy, and has between 8-12% THC.

That may be fine if you’re trying to draw conclusions about the health benefit of that one particular strain, grown at that one particular site. But if that sub-optimal product also has sub-optimal medicinal benefits, is it valid to conclude that all cannabis strains and products similarly don’t have medicinal benefits? Of course not. The inability to systematically test different strains and products—many of which have been optimized for certain conditions—has traditionally led to an inability for the clinical research to support many claims by cannabis patients.

A less-than-ideal solution to this problem is to simply survey patients about how various medicines affect their symptoms. In this manner, cannabis consumers can be compared to a cohort using a different form of medication, or no medication at all. But often, this is the only distinguishing feature.

There’s a wide range in the frequency and history of use, not to mention the type of cannabis consumed (only recently have some studies compared THC-rich cannabis to CBD-rich cannabis) or route of administration. Would you expect someone using cannabis to treat their anxiety by smoking THC-rich cannabis 4x/day to have the same response as someone using a CBD-rich tincture 2x/day to have the same effect? Most would say no.

Why do some reports say cannabis has serious side effects while others claim it’s safe?

There’s well-established evidence in rodents and humans that too much THC can induce acute anxiety, paranoia, and even psychosis. But it’s important to note that often, these effects occur with high-THC products with little CBD. After all, most strains’ THC levels have drastically increased over the last 20 years while CBD levels have decreased. While this carries its own risk, most medical cannabis patients are not consuming massively high doses of THC. Instead, the evidence suggests that they should be using a more balanced THC:CBD or CBD-rich product for treating the majority of conditions.

So what about CBD on its own? Supposedly it has minimal side effects, right? Well, it depends on what research study you read. The prominent phase III clinical trial of CBD treatment in a childhood epileptic disorder reported several side effects including diarrhea, fatigue, and somnolence. To some, those adverse effects are concerning. But is it CBD that is causing them directly? It’s unclear.

With clinical trials (such as the phase III epilepsy trial), due to ethical concerns, patients remained on their prescribed anti-epileptic medications. CBD was used as an “add-on treatment.” We know that CBD inhibits liver enzymes that are needed to metabolize other drugs, so it’s possible that some of the adverse effects are due to drug-drug interactions, and not CBD on its own. But at this point, we don’t really know, and broad research restrictions keep us from being able to figure it out.

A reader’s responsibility

It’s our responsibility to ensure that the published reports are valid. Often, positive reports of a drug’s benefits are highly scrutinized to confirm that the treatment was truly effective. For instance, many of the tests used to assess pain require the animal to move in response to a painful stimulus. But if THC has sedating effects, it can make it seem like it reduced pain when in reality, the animal was just lethargic. This is not to say that cannabis doesn’t reduce pain (loads of evidence in rodents and humans suggest it does), but we must be careful.

But in cases where the drug was ineffective, we must also apply the same level of scrutiny. Is it possible that the drug could have had a positive treatment effect that was masked by poor methodology? The cannabis field is ripe with these examples.

The strongest cases have an established mechanism at the cellular level, a pre-clinical effect in rodent models of disease, and supporting data from clinical trials. These cases are emerging for numerous disorders and will continue so at an even faster rate thanks to the effort of scientists in countries with fewer cannabis research restrictions than the United States.

Josh Kaplan's Bio Image
Josh Kaplan

Josh Kaplan, Ph.D., is an Assistant Professor of Behavioral Neuroscience at Western Washington University. He is a passionate science writer, educator, and runs a laboratory that researches cannabis' developmental and therapeutic effects.

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