IN TIME, some researchers themselves, among them psychologists Dr. Stanton Peele and Dr. Bruce Alexander, began to raise these questions. Peele's work on alcoholism has won him several awards, including the 1994 Alfred Lindesmith Award for Achievement in the Field of Scholarship from the Drug Policy Foundation in Washington, D.C. and the Mark Keller Award for Alcohol Studies in 1989 from the Rutgers Center of Alcohol Studies. Alexander, a professor at Simon Fraser University, has had less recognition, but Peele apparently agrees with many of his views on the "drugs-cause-addiction" hypothesis.

As both men have noted in separate studies, the only real evidence for the belief in drug-induced addiction comes from the testimonies of addicts who believed a drug caused them to lose control, as well as the lab experiments involving animals. But what if the lab animals were merely responding to their environment? And as for the addicts, Peele asks, "By rationalizing their intractable problems, are addicts merely escaping the enormous burden of guilt for their catastrophic lives?"

Indeed, if drugs were so naturally addictive, how do we explain the fact that doctors who give their patients large doses of opioids to manage their pain find that the bodies of these patients become dependent on the substance, but they do not become addicted? About 20 years ago, a U.S. research team began experimenting with a bedside self-medicating machine programmed to deliver about one mg of morphine intravenously to patients who pressed a hand button. But even without doctor's supervision, patients did not exceed the doses they needed for their pain, and did not become addicted.

Even outside the supervised setting of a hospital, people have drifted in and out of drug use, or even addiction. Another of my friends, D----, declares, "Sure, I take to the tooter once in a while, when we go out with friends. But now that I have children to support — two sets, actually, one set from my first marriage — I don't do it as often. I like the high I get, but I don't crave it…No, I don't consider myself an addict."

D--- has been employed for the last eight years by the same international organization. Before that, he worked with a government office. He has been regularly employed for over 20 years. I know he snorts up shabu more frequently when he has problems, and only occasionally when he doesn't. He may be suffering from denial, but I have come across several studies done on drug users in different parts of the world that show his "in-out" experience is not that unusual. Alexander even asserts that drug-induced addiction is "a myth." In a speech before the Canadian Senate in 2001, he went as far as calling it the "pharmacological version of the belief in 'demon possession' that has entranced Western cultures for centuries."

In 2004, the World Health Organization released a report called "Neuroscience of Psychoactive Substance Use and Dependence." The report, which capped an explosion of advances in neuroscience in the early part of the 21st century, concluded that substance dependence is a disorder of the brain like other neurological or psychiatric disorders. It said addiction or substance dependence could be caused by many factors, and that psychosocial, cultural, and environmental factors play a part in its creation. But it also asserted that addictions are determined largely by biological and genetic factors.

AS THE report explained it, psychoactive substances like drugs and alcohol are able to mimic the effects of neurotransmitters that occur naturally in human brains. Eventually, these drugs interfere with normal brain functioning by altering how these neurotransmitters are stored, released, or removed.

Drugs may be depressants like alcohol, sedatives, volatile solvents; stimulants like nicotine, cocaine, amphetamines, ecstasy; opioids like morphine and heroin or hallucinogens like PCP, LSD and cannabis — and all these have different ways of acting on the brain to produce their effects. Different drugs cause different behaviors. Tolerance to them develops at different rates as well, and withdrawal from them causes different symptoms.

But what these different drugs have in common is that they all affect the region of the brain involved in motivation. When such drugs are repeatedly taken, they repeatedly activate the motivational systems of the brain that are normally triggered by things that are important to human survival, such as food and water. With each exposure, the association becomes stronger and stronger, and the brain is "tricked" more and more.

Addiction is also "learned": A person takes a substance and experiences the "high." Because a high is, well, highly rewarding or reinforcing, it activates circuits in the brain that will make it more likely that the user will repeat whatever it is that gave him the rush in the first place.

This "associative learning process," combined with the brain being "tricked" into believing it needs the drug for survival cause a craving so overwhelming that it can "cause relapse to substance use, even after long periods of abstinence," the WHO report says.

Genetics is the other factor. In truth, even outside of the report, there has been growing evidence that some people may be more predisposed to addiction to cigarettes, alcohol, and opioids, so much so that scientists are now deep into the study of which specific genes are involved.

At its simplest, this is what the WHO report seemed to be saying: In many cases, addictions can be traced to damaged neurotransmitters in the brain or to some brains being more genetically susceptible into being tricked into thinking opium is food, or shabu is water.

Still, it did say there are other factors to consider. In fact, many experts argue that it is pointless to discuss only what gene X does — or even what genes X and Y do — without considering the role of environment Z in the mix.

To help find out whether it is genetics or environment that determine behavior, some behavioral geneticists have "cross-fostered" monkeys. They took monkeys from a group demonstrating a certain behavior that was totally unacceptable in another group, and threw them into that other group. The monkeys, given just a few moments to learn a new response in their new environment, adapted the new behavior — even when it was the opposite of the behaviors they had previously considered as appropriate and that was supposedly deeply imprinted in their genes. In this case, environment won over genes.

The way Peele sees it, "everything about the disease approach — from separating people and their substance use from their ongoing lives, not recognizing that addiction fades in and out with life conditions, viewing it as biogenetic in origin" — is wrong.

Historian Virginia Berridge and psychiatrist Griffith Edwards also examine the social and medical history of the addiction concept as it developed in England in their book Opium and the People: Opiate Use in Nineteenth-Century England and conclude, "Addiction is now defined as an illness because doctors have categorized it thus."