Study: smoking cannabis causes less DNA damage than smoking tobacco

Cannabis consumption is less likely to cause DNA alterations than tobacco consumption, according to a new epigenetic study recently published in the journal Translational Psychiatry.

The genes play an important role in the reaction of individuals to specific drugs, while influencing the possible onset of dependence. Drug use is also known to bring temporary or permanent changes to a user's DNA through a process known as DNA methylation.

DNA methylation is a biological process in which methyl groups are added to a DNA molecule, creating a signal that can deactivate a specific gene. Scientists believe that errors in this methylation process can make an individual more vulnerable to diseases such as cancer, lupus or muscular dystrophy, or make them more likely to pass on birth defects to their children.

Environmental factors such as drug or alcohol use, stress, diet, exercise and bacterial infections can also alter the normal methylation process, increasing the risk of disease. Some of these changes appear to be permanent, while others are dynamic and temporary. For example, studies show that higher levels of DNA methylation are seen in tobacco smokers, but these changes can return to normal if they stop.

The study

A team of New Zealand researchers set out to discover how cannabis alters the DNA methylation process, compared to tobacco. The researchers used data from the Christchurch Health and Development Study, a longitudinal study that followed 1,265 children born in 1977 throughout their lives. These subjects were studied 24 times between birth and age 40, and researchers took a blood sample from most participants at age 28.

The present study involved 96 participants who submitted a blood sample and described their lifetime drug use. The researchers divided the group of subjects into two groups: those who used both cannabis and tobacco, and those who used cannabis only. For cannabis-only users, the researchers limited the subjects to those who had used it for three years or more, or who met the criteria for cannabis use disorder.

Using the blood samples, the researchers extracted DNA from each subject for analysis. The results linked cannabis to DNA methylation in a number of genes, but the results were less extreme than those caused by tobacco. «Consistent with previous reports on tobacco exposure, we observed the greatest differential methylation in cannabis with tobacco users in the AHRR and F2RL3 genes.», explain the study authors. «These changes, however, were not apparent in the cannabis-only group.»

However, cannabis use was linked to increased DNA methylation in genes not affected by tobacco. These genes are linked to neural signaling and cardiomyopathies, which could potentially explain how cannabis could increase the risk of mental illness or heart disease.

The authors conclude that «the effects of cannabis use on the mature human blood methylome differ from and are less pronounced than the effects of tobacco use, [...] larger sample sizes are needed to investigate this further».