Just as fans were filing into the Brickyard 400 NASCAR race last month, a big screen by the entrance displayed a pro-pot ad with the headline "A new beer?"

"If you're an adult who enjoys a good beer," the ad said, "there's a similar product you might want to know about, one without all the calories and serious health problems. Less toxic so it doesn't cause hangovers or overdose deaths. And it's not linked to violence or reckless behavior. Marijuana. Less harmful than alcohol and time to treat it that way."

An effort is currently under way in Florida to get a proposed medical marijuana constitutional amendment on the 2014 ballot. People United for Medical Marijuana has collected enough voter signatures to trigger a Florida Supreme Court review of the proposed amendment language.

So is marijuana "less toxic" than alcohol?

"I don't see how this could be a more open-and-shut case," Mason Tvert, communications director for the Marijuana Policy Project, which produced the ad, told PolitiFact Florida in an email. "If you consume too much alcohol in a sitting or over the course of your life, you can die. If you consume too much (marijuana) in a sitting or over the course of your life, you do not die. What more could be needed to prove marijuana is 'less toxic' than alcohol?"

Some health professionals say it's a matter of picking your poison.

"It's like trying to compare different weapons. Both have the potential to cause harm," said Dr. Scott Teitelbaum, professor and vice chairman of the Department of Psychiatry and chief of the Division of Addiction Medicine at the University of Florida. "I don't know that there's a clear answer."

For starters, the term toxic can be vague. Dr. Cynthia Lewis-Younger, medical director of the Florida Poison Information Center in Tampa, said toxic can be "anything that causes harm. It is possible to drink enough water to poison yourself. It's more related to the dose than anything else."

The Marijuana Policy Project's claim that marijuana is "less toxic" rankles some health professionals and antidrug organizations who criticize the inference that using the drug is okay.

Calvina Fay, executive director of the Drug Free America Foundation, said she wants the public to realize that "these are two drugs that are both addictive and impairing and they both create unsafe situations."

Briefly, here's a look at how the National Institute on Drug Abuse describes each.

Alcohol is produced by the fermentation of yeast, sugars and starches and while it may start as a stimulant in small doses, NIDA describes it as a central nervous system depressant that is rapidly absorbed from the stomach and small intestine into the bloodstream. Intoxication can impair brain function and motor skills, and heavy use can increase the risk of certain cancers, stroke and liver disease.

Marijuana is a dry, shredded green and brown mix of leaves, flowers, stems and seeds from the hemp plant Cannabis sativa. The main psychoactive (mind-altering) chemical in marijuana is delta-9-tetrahydrocannabinol, or THC. When marijuana is smoked, THC rapidly passes from the lungs into the bloodstream, which carries the chemical to the brain and other organs.

Activists on both sides can find studies to back up claims about the health impact of weed.

NIDA states in an email that the effect of marijuana can depend on the biology of the person who's using it, the amount and under what circumstances.

"Claiming that marijuana is less toxic than alcohol cannot be substantiated since each possess their own unique set of risks and consequences for a given individual," according to an agency email statement.

Statistics certainly paint a grim picture of the lethal impact of alcohol abuse.

The Centers for Disease Control's National Center for Health Statistics reports that there were 41,682 deaths attributed to alcohol in 2010, the last year with the most exact statistics. That breaks down to 15,990 deaths attributed to alcoholic liver disease and 25,692 other alcohol-induced deaths, excluding accidents and homicides. The center doesn't have any reports with marijuana listed as a cause of death.

"Alcohol in excess is probably the No. 1 cause of toxicities from drugs of abuse in the world simply because it's most widely used," Lewis-Younger said.

Robert Gable, a retired professor of psychology at Claremont Graduate University in California, compared the toxicity of 20 abused substances using reports of experimental human and animal research and on published data of overdose fatalities.

He compared the drugs by developing a safety ratio — the ratio of an effective dose (eliciting a "relaxed affability") to a lethal dose.

"Two drinks make you buzzy; 20 drinks put you in the emergency room or the morgue," Gable said in a phone interview. "Ten is the safety ratio" for alcohol, among the most toxic recreational drugs, he said. The least physiologically toxic substances — those requiring 100 to 1,000 times the effective dose to cause death — included marijuana when ingested. He couldn't find any cases of documented deaths from smoked marijuana "so the actual dose is a mystery."

"No drug is good for teenagers," he said, "but when it comes to the chances of immediate death by chemical toxicity, marijuana is about a hundred times less toxic than alcohol or cocaine."

Experts say one concern is the impact of marijuana on the brain, particularly for teens who start smoking early. Teitelbaum says marijuana can "flip" adolescents predisposed to mental problems into having a psychotic disorder.

Another concern in recent years: the use of synthetic marijuana, often called Spice. Health professionals caution that it's vastly different from natural marijuana and more toxic.

Synthetic marijuana, however, is not marijuana.

Our ruling

An ad from the Marijuana Policy Project claims marijuana is "less toxic" than alcohol. Science and statistics present a strong case.

We rate this claim Mostly True.

Edited for print. Read the full version at PolitiFact.com/florida.