Genes play an important role in whether a person becomes addicted to drugs or alcohol, experts say, but they don't guarantee anything.
There are scientists studying the role of genes in addiction who believe that a single gene is not responsible for addiction. They say it's more likely the interaction of several genes, combined with other factors, which lead a person toward addiction.
Dr. Glen Hanson, a researcher with the University of Utah who studies genetics and its role in addiction, says that while some people are genetically prone to becoming an addict, it's not a given they'll become one.
“I think it's important to understand that because you're vulnerable doesn't mean it's inevitable,” Hanson said. “It just says that you got to be careful and that if circumstances are right, the chances that you'll get into difficultly are greater than most people.
“It's important to appreciate those. Then we can use them to our advantage instead of those things working against us.”
Hanson says there isn't a single gene that causes addiction to drugs and alcohol. He says researchers aren't sure exactly how many there are.
“This is a very complex genetic issue,” he said. “It's not like there is an addiction gene, end of story. It's probably like there's 50 or 100 genes that can give you vulnerability under a variety of different settings or issues.”
The different ways people react to drugs, individual decision-making abilities and what started a person drinking or using show that genes are involved, Hanson said.
“Why would you continue to use it even though you appreciate it could have some serious negative consequences ... that's probably some of it coming from genetics,” he said. “Some people are good at making decisions, even as teenagers.”
Charles Joseph Shaw, a medical doctor who deals exclusively with addicts in Oklahoma City, said he's seen Hanson's theories on genes and addiction play out in real life.
“The genes always get you, in the end,” Shaw said. “I see that all the time in my practice at St. Anthony's.”
Shaw said one of the first things he asks a patient is whether they have any family members who struggle with addiction.
“It's amazing,” he said. “Most all of them do. Sometimes it skips a generation, but if one or both of your parents has an addiction, you could have the gene, so to speak. That's why some people have to be careful while others can take it or leave it.”
Hanson said people become addicted to drugs and other substances because of the way they interact with the brain.
“Virtually all of the drugs of abuse have one thing in common, as far as the neurobiology goes,” he said. “Every one of them activates a dopamine system.”
Dopamine is “a critical neurotransmitter in the brain, and it's associated with some very vital functions,” Hanson said.
Pleasure and reward systems are two of those.
“If I were to wipe that dopamine pathway out of your brain, you'd never feel good, life would be rotten and you'd probably commit suicide,” Hanson said.
Repeated use of the same drug can lead to a tolerance in some individuals, causing them to gradually increase their dose to achieve the desired effect.
And once the mind is hooked, the body soon follows in the form of withdrawal symptoms, which commence soon after an addict's last high begins to wear off.
Withdrawal from opiates, for example, can include “restlessness, muscle and bone pain, insomnia, diarrhea, vomiting, cold flashes with goose bumps and involuntary leg movements,” according to the National Institute on Drug Abuse.
Because of the mental and physical characteristics of addiction, many scientists and other health authorities say it's a chronic, complex disease.
According to the institute's website, the disease typically begins to develop during adolescence.
An institute report states that during these key developmental years, a young person's brain is still in the final stages of growth.
“The prefrontal cortex — located just behind the forehead — governs judgment and decision-making functions and is the last part of the brain to develop,” the report states.
“This may help explain why teens are prone to risk-taking, are particularly vulnerable to drug abuse, and why exposure to drugs at this critical time may affect propensity for future addiction.”
Hanson said scientists are studying the relationship between genes and addiction because there are roughly 100 genes associated with addiction.
“This means that the cause can vary from person to person,” he said. “If we know what the cause is, we can be more selective with our treatments and likely more effective.”
Another reason scientists and researchers are studying the link between genes and addiction, Hanson says, is to allow medical professionals to be more proactive when dealing with drug and alcohol addiction.
“It is likely that this information would make our prevention strategies more targeted and more likely to succeed,” he said.
Scientists also are studying addictive behavior in mice to help identify which genes are involved in the process of becoming addicted.
Mice and humans are very similar, genetically, and mice exhibit varying levels of addiction in lab tests.