Benefits from a marijuana tax? California is dreaming.

Backers of the November ballot initiative to legalize marijuana in California are selling the idea based on economics: The state is in dire financial straits; taxing and regulating the drug – much like alcohol – could raise $1.4 billion for state coffers.

That estimate comes from the California Board of Equalization, which administers the state's sales taxes. The source gives the economics argument an air of credibility. Even so, voters shouldn't inhale it.

The board's estimate "is based on a series of assumptions that are in some instances subject to tremendous uncertainty and in other cases not validated," said Rosalie Liccardo Pacula of the RAND Corporation, in testimony before the state Assembly. Dr. Pacula is an economist who has studied drug policies for 15 years.

One of the highly questionable assumptions is that a legal market can sustain a proposed $50-an-ounce tax on marijuana. The black market can easily undercut that tax, siphoning sales away from legal distributors and eroding tax revenues.

This is exactly what happened in Canada with cigarette taxes. In the 1990s, a mere $2 price difference between Canadian and US cigarettes created such a smuggling problem that Canada repealed its tax hike.

And then there are the costs that will be incurred with increased use – and legalization will drive use.

These costs relate to treatment of dependency (over a third of self-reported users of marijuana in the past year are dependent), missed and tardy work, drugged driving accidents, and increased crime.

The Netherlands, so often pointed to as the reasonable case for legalization, has discovered that normalizing marijuana increased dependence on the drug, spawned more dealers of harder drugs, and attracted a flood of rowdy "drug tourists" from other countries. Add to this the cost of regulation itself.

America's experience with alcohol and tobacco shows that health, lost productivity, and law enforcement costs far exceed tax revenues. These industries have not managed to keep their products from young people. A legal pot-smoking age of 21 would similarly fail to keep this drug away from youth.

Other states, such as Washington, Oregon, and Nevada, are looking at regulating and taxing marijuana. The budget argument is enticing. But economically, and in many other ways, legalizing pot does not add up.