Could there be a genetic link that makes people who smoke more likely to drink and take recreational drugs?
Researchers at Bristol University had a look at the genetic profiles of more than 120,000 people and discovered smoking cigarettes is a ‘gateway drug’, but cannabis and alcohol can’t be described in the same terms.
DNA is composed of sequences of four proteins known as nucleotides. Single Nucleotide Polymorphism (SNPs) are a difference of one nucleotide in a string of DNA to the sequence that it is supposed to have.
There can be 5 million such ‘spelling mistakes’ in the average human genome, and 100 million across the whole of humanity. Where they are found in a gene, they can make it act slightly differently to the way other ‘correctly spelled’ genes work.
SNPs are most commonly found in strands of DNA that aren’t genes, and can help scientists locate genes that are linked to things like, in the case of this study, whether someone is more likely to take drugs.
The Bristol University team were able to locate 378 SNPs associated with smoking, 99 with alcohol use, eight that were associated with cannabis use and one associated with cocaine dependence. They found no SNPs associated with opioid dependence or cannabis dependence.
The research was a statistical analysis looking at the 120,000 people whose genomes had been sequenced, and who had reported that they smoked, consumed alcohol or took recreational drugs.
Using ‘Mendelian Randomization’ they tried to assess the following links:
Smoking cigarettes and
They also looked at the links between alcohol and:
Finally they assessed the biological links between cannabis and
Their interest in this research was the strength of the evidence as opposed to an effect estimate. Essentially, how strong are the associations they discovered?
From this research they hoped to find a definitive link that supports the idea that cigarettes, alcohol or cannabis are a ‘gateway drug’ as so heavily claimed by certain parts of the political establishment and society at large.
The research showed the following strong links between the use of the drugs assessed.
If you are a cigarette smoker you will be more likely to:
Smokers will not however be more likely to be cocaine or opioid users.
If you are a cannabis user you will be more likely to smoke cigarettes. This is what the research paper referred to as a ‘bidirectional link’ and we will discuss this later.
There are no ‘gateway markers’ between cannabis and alcohol, opioid or cocaine dependency. Nor did the research find direct links between alcohol use and smoking, cannabis (use or dependency), cocaine dependency or opioid dependency.
Where it comes to biological links between predispositions to taking one drug or another, people who smoke cigarettes are more likely to consume other drugs including alcohol and cannabis.
Though a lot of people wanted to believe that cannabis is a gateway drug, this research only predicts that you will become a cigarette smoker if you use cannabis.
The discussion of the paper pointed out that this has previously been believed to be due to the fact that many people consume cannabis with tobacco in joints – but they have shown biological markers as well. This research showed gene markers common to cannabis users and smokers.
The research also highlighted that some of the SNPs they found may be linked not to smoking cigarettes but to risk-taking. Other research has linked cannabis use to risk-taking and even the presence of ADHD in the user.
Risk-taking has biological markers, but given the necessity of taking risks in a positive way to advance the species as a whole isn’t always a bad element to have in your genome!
This was the first piece of research to use Mendelian Randomization to assess the links between biological markers for different drug uses. It was hampered by the numbers of genomes from those with reported opioid, cocaine and cannabis users.
The authors admitted that this could have impacted the quality of the research they undertook.
When a piece of research is assessed for its quality, the numbers in a cohort are often referred to. In this case, the genes of over 1,200 people were assessed, but very few had reported using the recreational drugs that this looked at.
After a paper has been published, the next thing for other research teams to do is to try to repeat the research and get similar results to reinforce the evidence or challenge it.
Given that many states in the US and the whole of Canada has legalised cannabis use, the question that could be interesting is whether more people submitting their genes for sequencing may admit to cannabis use?
Thanks to cannabis, cocaine and opioid dependency being illegal, there may have been numbers of people who did have those issues who did not report such personal choices.
Another issue that the authors of the paper raised was that genetic markers are all well and good, but the environment will play a role in someone’s life too. Success or failure in life is as much a consequence of where you were born and whom you were born to.
Great parenting can steer someone away from the ‘bad crowd’ as they grow up. If the parents are only able to live in a tough neighbourhood due to their income it will be a harder job to get the child into the right school and into a good career.
If they were wealthy and as devoted to their children, in most cases the child will do far better in life than their poor equivalents.
A risk taker in a stressful situation exposed to cigarettes may choose those, while a risk taker exposed to an opportunity to make them rich in a different environment may choose that. No one grows up dreaming of becoming a heroin addict or alcohol dependent but many do to escape the pain of the experiences they have had in their lives.
Given these situations described, gene research can only describe a small part of human existence. While interesting that some cigarette smokers may be more likely to choose to smoke cannabis or to drink too much too often, ultimately they must choose to make those decisions themselves.
Someone with the genes to become dependent on cocaine may never encounter the stuff due to the life they have led! Many people with parents who have had alcohol dependency choose not to drink alcohol so they don’t have the same issues in life they saw in their parents.
Ultimately, genes may guide certain decisions but won’t necessarily guarantee that those outcomes will occur. The environment will be the final arbiter of that.
Boris is our editor-in-chief at Rehab 4 Addiction. Boris is an addiction expert with more than 20 years in the field. His expertise covers a broad of topics relating to addiction, rehab and recovery. Boris is an addiction therapist and assists in the alcohol detox and rehab process. Boris has been featured on a variety of websites, including the BBC, Verywell Mind and Healthline. You can connect with Boris online at LinkedIn or X.com.
