Mark, I don't argue that drug policy is futile, at least in the sense that you mean, or that it doesn't have an effect on drug use. It does. The price of a drug certainly has an influence over the rate of the use of that drug.

The three most important factors that influence use are price, availability and perception of a drug's harmfulness or attractiveness, but many other factors unique to time, place and culture also come into play.

But let's stick to your coke example and run through the three biggest factors that influence its use. 1). The drug war has largely failed to make it unavailable. (Certainly, if cocaine were legal, it would be comparatively more available than it is now, so that's worth considering.) 2). The drug war has also failed in its goal of keeping cocaine and other drug prices high. Cocaine is much, much cheaper than it was in the early '80s, despite a 25-year war against it. 3). And coke is still considered to be a very attractive drug, but also one that has a considerable down side.

So the drug war has largely failed in its first three goals and left in its wake millions of lives shattered by enforcement policies. That needs to be considered in the context of the negative consequences of legalization.

I'm not arguing that cocaine use wouldn't increase if it were legalized. It probably would. But I'd challenge some of your assumptions about what the legal trade would look like. Why would alcohol and cocaine have to be on an equal regulatory footing? We have agreed that it's good policy to prevent tobacco ads from airing on TV. We could similarly circumscribe cocaine advertising. In exchange for a federal license to manufacture cocaine, a producer could be required to agree to tight restrictions on advertising - perhaps an outright ban other than a website.

And to use your tax policy example, it would also be reasonable to heavily tax cocaine to keep the price very high. (Plus, every time a Wall Street guy and his three buddies go to the bathroom together, the U.S. treasury takes in a few hundred bucks more.) The stated goal of U.S. drug policy is to reduce consumption by increasing the price through a combination of reducing supply (enforcement, interdiction, eradication) and reducing demand (treatment, education). It would be smarter (and more humane) to influence the price using a combination of tax policy and investment in treatment and education.

Now that we're talking about the relationship between tax policy, price, and use, I'd point out that you've ceded major ground to the legalization side. We're now debating what the most appropriate way to regulate cocaine is. If we find that the tax isn't sufficient to tamp down consumption, we could increase the tax further, which would have the added benefit of raising additional revenue that could be used to fund addiction treatment and an education campaign about the very real risks associate with cocaine.

To be an advocate of legalization, one need not argue that drug use wouldn't go up, but rather that a possible increase is outweighed by the possible benefits of legalization - fewer prisoners, more revenue, more treatment. If use does rise under legalization, remember that that down side needs to be balanced against the consequences of prohibition: thousands in prison and millions whose lives are made more difficult thanks to a drug charge. There are 800,000 people arrested every year for marijuana, after all, who would be better off without that charge on their record. So I would put it back to you this way: Why is prohibition a better strategy to increase price than the one laid out above?

You also write:

"The book also pays a lot of attention to substitution effects, which, you say, makes drug policy a mere game of 'whack-a-mole.' But substitution is only one of two logical possibilities: the other is complementarity... Basically, any stimulant (cocaine, amphetamines, methylphenidate, caffeine) complements any depressant (alcohol, opiates, benzos, barbiturates): think of rum-and-cola or cafe royale, or someone taking a drink or a Valium to get to sleep after a speed or coke run. Roughly speaking, stimulants keep you awake to enjoy more and more of your favorite depressant, and depressants help you come down from your favorite stimulant. More surprisingly, the depressants seem to potentiate one another. Casual drug users are sometimes specialists, but heavy drug users, other than some alcoholics, tend to be generalists. So when people tell me that easing up on drug laws would merely shift drug users around among drugs without increasing the total number of people in trouble, I have to scratch my head. Increased consumption of cocaine would almost certainly lead to increased alcohol abuse."

A couple things here. First, you're conflating a macro analysis with a micro one. You're talking about the specific choices of individual drug users. But in the aggregate, on a macro level, when one drug has become less popular or less available another has often become more popular, more available. Take the reduction in drinking that began in the 1830s and extended over the next several decades. At the same time, opiate use increased. So much of the effort of the temperance movement was for naught.

Importantly, though, I don't argue that legalization wouldn't increase drug use. It would, I think. (Although this Zogby poll found 99 percent of people saying that if hard drugs were legalized, they still wouldn't do them. A few of them are lying, of course, because more than 1 percent of the population already does hard drugs.)

My point, rather, is not that LIBERALIZING drug policies would cause people merely to shift around, it's the reverse: I argue that TIGHTENING policy around a specific drug (say, marijuana in the early '80s) can raise its price or make it less available and lead folks to use something else (say, cocaine) in the aggregate. To be sure, not every individual responds that way, but enough respond that way overall to undermine the overall policy.

I also don't believe that drug policy is "a mere game of 'whack-a-mole." It often is a game of 'whack-a-mole,' but it is also much more than that. It is the ability of drug users to substitute one product for another, however - the 'whack-a-mole' effect -- that makes drug policy so complex and so difficult and leads to so many unintended or unforeseen consequences.

And it's been that way from the beginning.

An 1872 study into the rise of opiate use in America by the Massachusetts State Board of Health, which I write about in my second chapter, concluded that the "most important cause" of the rise of opium was "the simple desire for stimulation." It was the temperance movement that had made alcohol uncool. Opium, however, "can be procured and taken without endangering the reputation for sobriety. In one town mentioned, it was thought 'more genteel' than alcohol." The report goes on to note "between 1840 and 1850, soon after teetotalism had become a fixed fact, that our own importations of opium swelled." The report noted as an aside that it was "curious and interesting" that as wine drinking increased in Turkey, use of opium retreated.

The real point of my 'whack-a-mole' argument isn't to suggest that drug policy is futile. Rather, it's to say that its consequences are wildly unpredictable. The reasons people get high are many and varied: price is among them, but so is societal pressure, compatibility of a given drug with a given lifestyle, and a person's own consideration of the many costs of drug use versus the benefits - a calculation heavily influence by a person's station in life and hope for their own future. (The more hope for a vibrant future, the greater is the disincentive to become an addict.)

The great risk of legalization is a drastic increase in drug addiction, which could shatter thousands of lives. But by tightly regulating and steeply taxing hard drugs - and only doing so after the very gradual legalization of marijuana, a strategy I can elaborate on in a later post -- those risks could be somewhat mitigated. If they're not, I argue in my book that the point will be moot. Our history shows that if we did legalize drugs and people had ready and cheap access to them, we'd go on a college-freshman binge, wake up a few years later and ban everything all over again.

I've been arguing from a public-health policy perspective here, but let me add something else I believe, though I don't make this argument part of the book: It should not be, from a moral perspective, a crime punishable by imprisonment for an adult to voluntarily choose to consume a drug.