And, in a bonus edition of 'Science Diction,' Dr. Markel explains the origins of the word 'addiction:'

The now familiar medical diagnosis of "addiction" did not really exist until the late 19th century. The earliest use of the word was as an edict of Roman law. In antiquity, "addiction" referred to a bond of slavery that lenders imposed upon delinquent debtors or victims on their convicted aggressors. The offending individual was mandated to be "addicted" to the service of the person to whom they owed restitution.

From the 1500s on, the word was employed for those compelled to repeatedly act out any number of habits including gluttony, obstinacy, and even too much reading. By the 18th century, addiction occasionally signified the overconsumption of tobacco and alcohol. But it was the 19th century that witnessed the beginnings of its modern definition thanks to the over-prescription of opium and morphine by doctors to ailing patients. Soon after, doctors appropriated the words addiction and addict to describe "opium or morphine-eaters" who simply could not "kick" their habits.

Derived from the poppy, a red wild flower that flourishes in Turkey, Afghanistan, China, Asia Minor, and the Middle East, opium was the first transglobal pharmaceutical agent in the history of medicine. The more potent morphine was chemically derived from poppy sap in 1803. Named after Morpheus, the Greek god of dreams, the drug began to be mass marketed in the 1820s. Especially after the development of the hypodermic needle-syringe in 1853, there was an explosion of doctors freely prescribing and patients readily taking and abusing opium, morphine, and later codeine and heroin.

In 1884, the Detroit pharmaceutical house, Parke, Davis and Company, began pushing their latest miracle drug, cocaine. It was heralded as a sure-fire painkiller, an anodyne for depression, and even a morphine addiction cure. One of the leading advocates of this last use was a neurologist named Sigmund Freud.

Substituting one addictive drug for another was a common medical means of treating substance abuse in the late 19th century. It is impossible to quantify how many morphininists were unwittingly turned into cocaine addicts during this era; similarly, alcoholics were often prescribed morphine and tobacco to help them kick their drinking habits. At the dawn of the doctor’s recognition of addiction as a disease, what all these games of medical musical chairs most reliably did was to create "new and improved" addicts. One of the most tragic victims of this therapeutic approach was the master surgeon, and creator of the surgical rubber glove, William Halsted.

In the century that followed, a revolution has occurred in our understanding of addiction to mind-altering substances. Today, many experts believe that compulsive behaviors such as excessive gambling, hypersexual activity and overeating fit the disease model of addiction. Rather than a form of slavery, a nasty habit, or bad character, brain imaging studies have demonstrated that addiction is the neurological equivalent of an overloaded power switch. Once activated, an insurgency of bad judgment and risky behaviors hijacks the brain’s delicate circuitry, in exchange for brief, artificial states of well being.

In the years to come, it is certain that the definition—as well as the science and treatment—of addiction will continue to evolve in ways we cannot even imagine.