April 16, 2019

Can’t resist smoking weed? Your DNA may be weighing in.

100+ million Americans have tried weed in some form. A DNA element involved? CADM2: a gene that influences substance abuse and risk-taking.
Tomohiro Takano

Marijuana: why the hype?

It may be legal in some American states now, but that certainly doesn’t mean scientists fully understand cannabis or its uses. This psychoactive substance is known by many names: marijuana, weed, dope, grass, Mary J, ganja, blow, draw, skunk, spliff, hash oil, hashish, etc.; but it is all derived from one source: a small herb of genus Cannabis.

Up to 11% of the variation within people’s choices to use marijuana may be related to a number of genes within the DNA code.

Historically, cannabis was already used as a mind-altering substance back in prehistoric societies in Eurasia and Africa. The oldest record dates back to 440 BCE, in the writings of the Greek historian Herodotus, describing central Eurasian Scythians taking cannabis steam baths!

Today, medical marijuana is legalized in over half of the states. It's one of the most popular recreational drugs around the world, behind only alcohol, caffeine and tobacco. There is a whole industry springing up around recreational weed use, involving many cannabis strains and cannabis products.

In the United States alone, over 100 million Americans have tried cannabis in some form.

As more and more US states (California, Oregon, Washington, etc.) and entire countries (Canada, South Africa, Uruguay) legalize marijuana for recreational use, the number of people who can access it is increasing. But not all people who have access to it use it or have ever tried it.

So why is it that some people choose to try cannabis and others don’t? Why are some people content with occasional use, while some others are at risk for abusing cannabis?

How much of that choice is influenced by our environment and how much by our DNA?

Can my DNA lead me to use marijuana?

Up to 11% of the variation within people’s choices to use marijuana may be related to a number of genes within the DNA code.

So the likelihood to try, use and abuse cannabis substances is, in part, determined by your DNA.

With recent genetic advancements, scientists are now finally getting a glimpse on how our DNA code may be contributing to a person’s decision to use marijuana. Scientists were able to pinpoint the SNPs (DNA variants) that have been linked to cannabis usage by analyzing raw DNA data provided by companies like 23andMe.

So what SNPs are associated with the predisposition to use marijuana? In that new study, scientists identified 8 SNPs associated with trying cannabis at least once in life -- with close to 200,000 participants of European ancestry! Those 8 SNPs are located on chromosomes 3, 7, 8, 11, 16, and 17.

The top associated SNP is located in the CADM2 gene, which previous studies have found to influence traits like substance abuse and risk-taking.

Separately, they found 35 genes significantly associated with cannabis use. Some of these genes (including CADM2, LRRTM4, and NCAM1) are expressed in the human brain and make proteins that play a role in our nervous system. Similarly, previous studies have found these genes to be involved in substance dependence and mood disorders like aggression.

What does my DNA result mean?

If you’re wondering why your results say that genetically, you have a high likelihood of using cannabis, remember that that’s only reporting what your DNA predisposes you to!

Your DNA only accounts for up to 11% in your chances of using weed. Considering that a huge part of the likelihood of using cannabis is determined by non-DNA factors -- such as the country you’re in, how you were raised, and your personal opinion on cannabis -- it’s not unusual for your actual experience with cannabis to not align with your DNA results.

Obviously, people who hate marijuana are not going to smoke it regardless of what genes they carry, and people who carry none of the genes related to marijuana use can still enjoy using it. Similarly, if you’re in a country where merely trying cannabis can land you in jail, you likely wouldn’t think of trying it even if you’re otherwise someone who has a high openness to new (legal) experiences.

Lastly, even though cannabis use is a heritable trait, there is no one specific gene that 100% guarantees you’d use or not use cannabis. However, each of the genetic variants in the large group of associated genes do contribute in various ways towards vulnerability to substance use, in the larger context of personality.

Since many of those different genes act in the brain, they may modify your behavior through brain development during your youth or the action of hormones. For example, this may result in a personality type where even while knowing the risks and potential side effects of substance use, would choose to try it anyway, for the thrill of it or to satisfy their curiosity.

Links with substance use and mental health?

The research suggests that the genetic predisposition for cannabis use is associated with a broad profile of risk-taking, novel sensation-seeking, addictive substance-using, and a carefree personality.

Specifically, here’s what was found to be correlated with the SNPs identified for influencing cannabis use. There were significant positive correlation with:

Dependence on psychoactive substances, for example:

  • Cannabis
  • Alcohol
  • Smoking

Mental health traits, for example:

  • Schizophrenia
  • Bipolar disorder
  • Autism
  • ADHD
  • Other personality traits, for example:
  • Reduced anxiety
  • Reduced sense of subjective well-being
  • Reduced conscientiousness
  • Higher risk-taking behavior
  • Higher openness to new experience

It seems that what genetically contributes to less anxiety and conscientiousness also contributes to the search for new sensations and willingness to take risks.

But just because some things are correlated, it doesn’t necessarily mean one causes the other, or vice versa.

Does using weed cause schizophrenia? Or the other way around?

Let’s look at the strong correlation between cannabis use and schizophrenia diagnosis. The question here is: “Does the use of cannabis increase the risk of developing schizophrenia? Or, is it that people with schizophrenic tendencies are more likely to use cannabis?”

Using some fancy statistical tools, scientists found that cannabis use does NOT increase one’s risk of developing schizophrenia. Schizophrenics may simply be more inclined to use marijuana because of the disease itself, perhaps as a form of self-medication.

In plain language, you don’t have to worry about marijuana causing you to become schizophrenic! Simply using marijuana will not increase nor decrease your odds for schizophrenia.

Looking ahead

Marijuana has only recently started to be legalized and entered the mainstream conversation. Research on marijuana is just starting out and is in the very early stages.

While we know that many of the character traits related to marijuana use also make people more likely to take risks in general, new research in this area is still needed to find out how valid the initial findings are. In addition, we need to understand the underlying biology on why variations to these genes are linked with marijuana use, certain personality types and mental disorders. With genetics as a starting point, many other scientific fields like behavioral sciences and psychology are now also looking into the effects of cannabis use on humans.

What is YOUR genetic predisposition?

“Cannabis Use” is one of 125+ trait reports offered on Genomelink. If you haven’t already, check your DNA results for "Cannabis Use" and your overall genetic profile on Genomelink now! Just upload your AncestryDNA, 23andMe or MyHeritage raw DNA data to get started.

* The “Cannabis Use” trait report is only available on the Unlimited plan. Click here to learn more.

Tomohiro Takano
Tomohiro Takano
Co-Founder and CEO