“It’s an egg-and-chicken kind of thing,” said Dipak Sarkar, co-author of the study. “You drink and you want to stop, but stopping gets harder because you have an alteration of your gene that makes you more susceptible to drink.”

The findings bolster the idea that drinking or drug use even in adolescence can create lasting genetic change that will affect future children, researchers say.

“It’s pretty amazing that stressors like drugs can create genetic change,” said Bill Jangro, medical director for the division of substance-abuse programmes at Thomas Jefferson Hospital in Philadelphia. “It goes against what most people think.”

Most research in this area focuses on alcohol’s ability to change DNA, though studies show a similar effect from opioids, cocaine, cannabis and methamphetamine.

But “we don’t necessarily know the full ramifications of what this change means”, Jangro said.

Researchers in the field of epigenetics, which studies how the environment can affect the way a person’s genes are expressed, are avidly hunting for answers.

The basic idea of genetic change centres on evolution: genes that favour survival are passed on while others die out, a process that can take hundreds of thousands of years.

Epigenetics studies how environmental factors can cause more immediate change, within an individual’s lifetime and passed down to the next generation.

In the Rutgers study, researchers found the more someone drank, the more genetic change they exhibited. The alcohol influenced a process called methylation, which keeps a DNA sequence intact but uses a chemical tag to turn certain genes on or off.

It’s one of the ways environmental stressors – from alcohol and drugs to physical and emotional stress on the body – can cause genetic change.

Previous research showed drugs can cause DNA methylation on different genes.

Studies on opioids indicate that methylation of the OPRM-1 gene, which is responsible for opioid receptors in the brain, creates a tolerance to the drug – explaining at a biological level why people who use opioids crave greater amounts over time.

Studying certain types of DNA methylation can tell us whether someone has used drugs – a technique applied in forensic sciences.

Although it has long been seen that addiction can “run in families”, DNA analysis does not tell us whether someone is more likely to use drugs in the future.

That is the holy grail researchers are searching for, Sarkar said: a biomarker.

If certain changes in DNA methylation predispose someone to addiction, we could identify those individuals and create early interventions, Sarkar said.

But for now, that research is limited to rats.

Studies at Tufts University’s school of veterinary medicine found that male rats whose parents were given morphine developed a tolerance to morphine more quickly. Their female siblings showed increased sensitivity to the rewarding effects of opioids.

“Even limited exposure to opioids can have lasting effects across multiple generations,” the authors concluded, including the possibility that children will be predisposed to drug abuse.

“That’s always been the hope of all mental illnesses,” Jangro said. “That we would find a biological cause that is somehow reversible.”

In a 2018 paper that reviewed the most recent findings on DNA methylation and drug use, researchers from McGill University in Canada suggested methylation inhibitors could be used to treat addiction.

This would “target the epigenetic underpinnings of this condition rather than the symptoms”, they wrote. It could reduce the incidence of relapse by stopping the process that causes craving in the first place.

The possibilities are exciting, Jangro said. “But I don’t think it’s going to happen any time soon.”