Advocates of legalizing marijuana have been blowing a lot of smoke in the debate over California's Proposition 19.

For starters, there's the fiction that marijuana is no different from alcohol. Indeed, the difference in health effects is striking.

The benefits of moderate alcohol consumption - reduced risk of heart disease, stroke, gallstones, diabetes, and death from a heart attack - are well-documented. There's even evidence that alcohol helps keep the mind sharp as one ages.

No one has ever associated pot consumption with mental acuity. Quite the opposite: Marijuana use has been shown to impair memory and inhibit learning ability. Among students, marijuana use is strongly associated with lower test scores and lower educational attainment. Chemically, marijuana is more like "harder" drugs - cocaine, heroin, speed, and the psychedelics - than a glass of wine or a cocktail. One study found that extended use may even lead to psychosis.

There are physical effects, too. Lung researchers report that smoking a couple of joints does more damage than a whole pack of Marlboros, and contains toxic compounds like ammonia and hydrogen cyanide. For many, pot is addictive. A study in the Journal of the American Medical Association found that more than 30 percent of pot smokers were dependent on the drug to the point of demonstrating signs of withdrawal and compulsive behavior. Reports from drug-abuse help lines and treatment facilities show that marijuana addiction is a major problem.

Negative social effects abound as well. Take crime. Amsterdam shows what happens when marijuana is available, legally and in abundance. Amsterdam is one of Europe's most violent cities, and Dutch officials pin the blame on their liberal drug policies. A report by four government ministries finds that drug-related crime places a heavy burden on local authorities and that criminal organizations are increasingly muscling their way into the drug market, using it as a base for international operations.

As California debates legalization, Dutch officials are retooling their laws and shutting down marijuana dispensaries "to tackle the nuisance associated with them and manage crime risks more effectively."

Legalization hasn't helped the Dutch keep marijuana from minors either. Marijuana use is higher among children there than anywhere else in Europe.

Legalization also alters social norms. More Dutch children smoke pot because the social stigma against it has dissipated. The same thing will happen in California if Prop 19 is passed next month.

Prop 19 pushers argue that by taxing and regulating marijuana, the state will reap a tax windfall. But the act would let every landowner grow enough marijuana to produce 24,000 to 240,000 joints a year for "personal consumption." Who would pay the $50-per-ounce tax on marijuana (a 100 percent tax) when he could grow it himself or buy some (illegally) from a neighbor.

Regular tobacco does not carry its economic weight. In 2007, the government collected $25 billion in tobacco taxes but spent more than $200 billion per year to cover health and other tobacco-related costs. It is the same with alcohol: In 2007, governments collected $14 billion in alcohol taxes but spent $185 billion to cover health, crime, and other alcohol-related costs. The economics of legalized marijuana will be no different, and perhaps worse.

Then there are the practical problems of Prop 19. Homeowners growing pot in their backyards will become targets for pot thieves and attendant crime, just as areas immediately around medical-marijuana dispensaries have already experienced an uptick in crime. And there remains the very real fact that possession, cultivation, and consumption of marijuana are still crimes under federal law - an inconvenient truth the act simply ignores. What are federal law enforcement officers to do?

Legalizing marijuana would serve little purpose other than to worsen the state's drug problems - addiction, violence, disorder, and death. Nor will such legalization produce a tax windfall for the state; rather, it will end up costing Californians billions in increased social costs.

Sound public policy should be based on facts, not smoke.

Edwin Meese III is a former attorney general of the United States and chairman of the Heritage Foundation. Charles Stimson is a senior legal fellow at Heritage and author of Legalizing Marijuana: Why Citizens Should Just Say No.