Marijuana for ADHD – what’s the evidence?

Those of you who follow this website know that I frequently take down myths about the medical usefulness of marijuana. Let’s just say the evidence barely reaches the level of “sparse.” Recently, Tara Haelle pointed me to an article that trumpeted using marijuana for ADHD, attention deficit hyperactivity disorder.

ADHD is a psychological disorder in which the individual is unable to focus, is overactive, is unable to control behavior, or a combination of these, not appropriate for the age of the individual. Diagnosing ADHD is often difficult, because the differential diagnosis for the condition can be confused with or related to other emotional, psychiatric or neurodevelopmental disorders such as anxiety, major depressive disorder, and bipolar disorder.

There are some treatments available for ADHD, including stimulants such as the well-known medications, methylphenidate, or better known by its trademarked name, Ritalin, and Adderall, a mixture of two amphetamines. These stimulants are very effective for treating ADHD, but there are some risks to its use, and the effectiveness appears to lower over time.

So let’s look at marijuana for ADHD – it’s pretty weak, but let’s give it a good scientific skeptical analysis.

Marijuana for ADHD – the evidence

 

I was originally pointed to this recent article which claimed that “studies are showing weed could treat ADHD better and safer than Adderall.” Well, let’s look at that.

The story is based on an article (pdf) published in the journal Cannabinoids. The authors concluded that:

[infobox icon=”quote-left”]A 28-year old male, who showed improper behaviour and appeared to be very maladjusted and inattentive while sober, appeared to be completely inconspicuous while having a very high blood plasma level of delta-9- tetrahydrocannabinol (THC). Performance tests, which were conducted with the test batteries ART2020 and TAP provided sufficient and partly over-averaged results in driving related performance. Thus, it has to be considered, that in the case of ADHD, THC can have atypical effects and can even lead to an enhanced driving related performance.[/infobox]

The authors appeared to claim that cannabis appeared to treat ADD and ADHD by increasing the availability of dopamine, a neurotransmitter, in the brain.

But let’s look at this study carefully:

  1. The journal has an invisible impact factor, meaning the relevance of its articles is suspect, as they are rarely, if ever, cited by more important articles in the field.
  2. The journal, Cannabinoids, isn’t indexed in PubMed. That’s an indictment of the quality, right there.
  3. The paper is based on a case study of precisely one patient, a 28 year old male. On the hierarchy of biomedical research, case studies are among the most useless. They are not randomized or blinded, so the author’s bias clouds the conclusions. It’s almost impossible to derive any scientific evidence that supports cannabis’ use in treating ADHD from this case study.
  4. The paper was published over eight years ago, yet there hasn’t been one cite for the article in numerous other articles that examined cannabis and ADHD.
  5. In fact, a more recent, larger study (n=376) seemed to show quite the opposite result – ADHD symptoms in young adults appeared to be correlated with increased cannabis use. Although this study isn’t perfect, it is of much higher quality, statistics and methodology than a case study of one patient. Cherry picking scientific research, especially a one-off case study, to confirm a belief is just ridiculous.
  6. A search of “cannabis and ADHD” has no articles that provide any evidence that cannabis has any effect on ADHD. Most of the articles provide evidence that cannabis is “abused” by those with ADHD.
  7. The role of dopamine (and related dopamine receptors) in the pathophysiology of ADHD is extremely complicated. Dopamine has a role, but the up and down regulation of it in neurotransmission are both critical to ADHD. Cannabinoids have a dopamine-like compound, but it just looks like it. It is not regulated in the same pathways, and, because they are lipophilic, they are not very soluble in water, so they probably can’t affect dopamine very much. Most importantly, since the balance between the up and down regulation of dopamine may be part of the issue with ADHD, just randomly smoking marijuana, which has a wide range of potency, may actually cause the symptoms to increase.

Summary

 

The trumpeted article does not provide any evidence that marijuana can treat or alleviate symptoms of ADHD. None at all, unless you grasp at straws and believe that a one-off case study has some value, which it doesn’t.

Moreover, there is no evidence that smoking marijuana can affect the dopamine pathways that may have an important role in the pathophysiology of ADHD, which the authors proposed as the physiologically plausible mechanism of why marijuana had an effect in this one patient.

I remain troubled that marijuana advocates are trying to invent medical uses, despite the total lack of evidence supporting these uses. I’m assuming part of it is to convince the public that marijuana is useful, but the evidence, unless you love cherry picking, is lacking on so many levels.

Marijuana should be legal, because it’s just as dangerous as alcohol. If you accept one, why not the other? But don’t try to “prove” the miracle qualities of weed with junk science. Marijuana for ADHD –that dog won’t hunt.



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The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!