Say no to drugs, caveman style: Our ancestors may have been exploiting 'drugs' for very long periods of time - and it may have been essential for our survive.

Credit: Illustration by Barry Olive

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Rarely today is anyone out of reach of an addictive substance. Almost everyone likes a drink now and then. Many of us struggle to get by without a coffee first thing. Or how about the way a prescription drug can take the edge off our anxiety during a time of great stress … but some people don't merely use these substances, they can't live without them.

What makes one person an addict while another can easily put down the glass or forego the pharmacology?

Addiction is defined as continued use in the face of obvious harm. The circle of harm includes physiological damage to the addict as well as hurt and pain for the addict's family and friends. Health officials insist addiction is an illness that needs treatment and can be cured, but no one is quite sure exactly what this illness is all about.

Originally, scientists assumed addiction was a matter of psychological reinforcement. Certain substances produce a buzz, or remove physical or emotional pain, and so people often want more. Given that explanation, addicts were weak-willed hedonists who just couldn't get enough fun.

But in the 1990s, scientists began to understand that the pleasurable reinforcement wasn't simply unfettered hedonism, it was brain chemistry.

They focused on the neurotransmitter dopamine, which lifts mood and brings on euphoria. Ingesting alcohol and certain drugs takes people on a dopamine high, but when the chemicals wear off, some people's brain chemistry doesn't return to normal levels, it dips below, landing them in a 'dopamine deficit', and with increased craving for the lost 'high'.

According to Nora Volkow, Director of the U.S. National Institute on Drug Abuse in Bethesda, Maryland, addicts are also neurochemically incapable of making good decisions. She found that low levels of dopamine receptors are associated with lower glucose metabolism in the frontal lobe of the brain, the place that regulates decision-making and inhibition.

In the same way, low levels of the neurotransmitter serotonin are implicated in addiction because people with low levels of serotonin often have poor impulse control. And, as a result, they drink or take drugs to excess.

But this isn't to say that having a genetic predisposition for poorly regulated brain chemistry is always the factor that causes a person to become an addict. Compulsive substance abuse is also a human behaviour deeply affected by personal history and environment.

Using animals models, including rats and monkeys, researchers have discovered that how an animal is housed, who they socialise with, their rank in the group, and what kind of care they received as babies makes a difference in how they modulate dopamine and serotonin - no matter what their genetic make-up might be. For humans too, life experience influences who takes what.

In fact, most health workers now describe addiction as a 'biobehavioral disorder': a product of the influence of chemistry and experience on one another.

But if addiction is such a negative human experience, why are so many people addicts? Evolution may be at fault.

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