When I presented to the International Harm Reduction Association in Liverpool, I pointed out that the 1964 Surgeon General's Report (SGR) said that smoking was not addictive: "They didn't neglect to say smoking was addictive -- they devoted a chapter to explaining why smoking was not addictive -- that it was merely habit-forming. They said it caused psychic dependence."

The audience laughed, and chalked it up to the impact of the tobacco industry. "The researchers are bought and sold," people shouted out.

I said, "Sorry, that explanation doesn't pass the laugh test. The SGR branded smoking as cancer-causing, which led to a halving of the number of Americans who smoke (from 42 percent then to 21 percent now). Why would pro-industry people do that?"

In fact, when I announced smoking was addictive in 1975, in my book "Love and Addiction," where I also said relationships and gambling could be addictive -- I was roundly ridiculed. Through the 1970s, one thing was regarded as addictive -- heroin.

Back at Liverpool, people looked puzzled. Human beings aren't made up to comprehend why what they know to be true was once rejected by sane, sensible people -- scientists, no less. "Why didn't those idiots understand smoking was addictive?"

The definition of addiction shifts. It has shifted over history. It shifted in the 1980s, when cocaine and nicotine were labeled addictive. It shifted again in the 1990s, when marijuana was called addictive. It is shifting under our feet right now as the forthcoming edition of the American Psychiatric Association's diagnostic manual, DSM-5, has designated gambling as an addictive disorder.

I bet you're having trouble righting this in your mind right now. The addiction-labeling committee (there is no such thing -- just a substance-disorder one) is having trouble doing so. The head of the DSM-5 Substance-Related Disorders Work Group, Charles O'Brien, explained it this way: "Pathological gambling and substance-use disorders are very similar in the way they affect the brain and neurological reward system."

Huh? What does that mean? Is there actually an addiction button in the brain, one that lights up for some things and not others? No, they have a much more elaborate theory than that related to dopamine's effects on the brain -- and how certain substances and now activities -- stimulate dopamine production.

Really? Gambling does that, but sex doesn't? (They have "hypersexuality" in DSM-5, but that's somewhere else.) The delineation of addiction in DSM-5, which is only scheduled to appear in May 2013, already doesn't hold up and will be discarded by history, I believe.

All activities stimulate brain chemicals; no powerfully motivating activity can be said to qualitatively affect the brain in one way and others in other ways. If one did, it would have to be sex, which O'Brien et al. haven't gotten around to calling addictive. Oh, another activity that has a tremendous effect on brain systems is being with -- loving -- a maternal or other warm, emotionally rewarding person, or even animal.

So when is something addictive? It's addictive when we reckon a kind of preoccupation has significant negative effects, either on us as individuals, or on society (that's why they decided cocaine was addictive in the 1980s).

And that shifts for society over time, although we Americans have special, long-term weaknesses. For example, recently deceased psychiatric historian David Musto called heroin addiction "The American Disease." His book of that name describes how Americans decided firmly and finally that narcotics were addictive in the twentieth century, although opiates had been used traditionally for centuries without people noting the drugs as especially problematic.

But that's a whole other story, which I told in "The Meaning of Addiction."

Additionally, what is addictive shifts for most people as they mature, which the great addiction psychologist Charles Winick called "maturing out" back in 1962, which got me interested in studying addiction in the first place.

So the history and the future of addiction are built on shifting sand.