By Joseph Brownstein, Contributing writer 
Published: 01/22/2014 07:41 AM EST on LiveScience
The question of whether alcohol or marijuana is worse for health is being debated once again, this time, sparked by comments that President Barack Obama made in a recent interview with The New Yorker magazine.
"As has been well documented, I smoked pot as a kid, and I view it as a bad habit and a vice, not very different from the cigarettes that I smoked as a young person up through a big chunk of my adult life," Obama said during the interview. "I don't think it is more dangerous than alcohol."
But how apt is the comparison between these substances? While both are intoxicants used recreationally, their legality, patterns of use and long-term effects on the body make the two drugs difficult to compare.
Both alcohol consumption and pot smoking can take a toll on the body, showing both short- and long-term health effects, though alcohol has been linked to some 88,000 deaths per year, according to the CDC, while for a number of reasons those associated with marijuana use are harder to come by. And research into marijuana's health effects is still in its infancy, compared with the rigorous studies looking at alcohol and human health.
Short-term health consequences
Drinking too much alcohol can quickly kill a person. The inability to metabolize alcohol as quickly as it is consumed can lead to a buildup of alcohol in the brain that shuts down areas necessary for survival, such as those involved with heartbeat and respiration. [7 Ways Alcohol Affects Your Health]
"You can die binge-drinking five minutes after you've been exposed to alcohol. That isn't going to happen with marijuana," said Ruben Baler, a health scientist at the National Institute on Drug Abuse. "The impact of marijuana use is much subtler."
(Of course, subtle effects don't equate with no danger, as is the case with smoking cigarettes, which is linked with 440,000 deaths per year in the U.S.)
Marijuana affects the cardiovascular system, increasing heart rate and blood pressure, but a person can't fatally overdose on pot like they can with alcohol, Baler said.
Alcohol is more likely than marijuana to interact with other drugs. The way that alcohol is metabolized, or broken down, in the body, is common to many drugs that are taken for a variety of conditions, said Gary Murray, acting director of the Division of Metabolism and Health Effects at the National Institute on Alcohol Abuse and Alcoholism.
This means that for people taking drugs or medications while drinking, the alcohol can increase or decrease levels of the active drug in the body.
"Those things can make it very hit and miss, whether you're getting an active dose of a medication," Murray said.
Still, both drugs can affect health in indirect ways, too.
Because marijuana can impair coordination and balance, there is the risk of hurting oneself, particularly if someone drives or chooses to have unprotected sex while their inhibitions are lowered, Baler said. These are two areas where people using marijuana could hurt themselves for the short and long term.
Long-term health consequences
The long-term effects of drinking heavily are well known. "Excess alcohol is going to lead to very severe consequences, and chronic excess alcohol is the most likely to lead to a lot of threatening issues," Murray said.
Drinking can lead to alcoholic liver disease, which can progress to fibrosis of the liver, which in turn can potentially lead to liver cancer, Murray said.
"I emphasize 'can' – it's not even clear to the best scientists what are the triggers that allow that progression to happen," he said, noting that why some people have a higher risk than others of developing liver disease from drinking is not understood medically or biochemically.
Unlike alcohol, Baler said, the effects of chronic marijuana use are not as well established. Animal studies have indicated some possible impact on reproduction. Additionally, there is evidence marijuana can worsen psychiatric issues for people who are predisposed to them, or bring them on at a younger age. Finally, Baler said, because the drug is typically smoked, it can bring on bronchitis, coughing and chronic inflammation of the air passages.
But while early studies showed some evidence linking marijuana to lung cancer, subsequent studies have debunked that association. Baler said it's unclear why marijuana smoke does not have the same result as tobacco smoke on the lungs, but perhaps some beneficial compounds in the marijuana smoke cancel out the ill effects, or perhaps the other health habits of marijuana smokers are different from those of cigarette smokers.
But cigarette smoking plays a complicated role in studying the impact of marijuana smoke, Baler said. Marijuana smokers tend to smoke much less than cigarette smokers, as some may smoke one joint a few times a week.
"It's a very tough epidemiological nut to break," Baler said.
Additionally, researchers looking to study long-term marijuana use have had difficulty in finding people who regularly smoke marijuana but don’t also smoke tobacco cigarettes. And the illegality of marijuana has also limited research in this field.
For marijuana, much of the concern is with young people who use the drug, because the drug interferes with the development of the brain while it is still maturing, Baler said. [10 Facts Every Parent Should Know About Their Teen's Brain]
Smoking marijuana interferes with connections being made in the brain "at a time when the brain should be at a clear state of mind, and accumulating, memory and data and good experiences that should be laying out the foundation for the future," Baler said.
"How much you're impaired depends on the person, and how much you smoke," Baler said. Because some people are stoned a lot of the time, while others may use marijuana only on weekends, the health effects become difficult to generalize.
"You're cumulatively impairing your cognitive function. What's going to be the ultimate result, nobody can say."
Benefits
There is no known medical use for consumed alcohol, but there are health benefits observed in moderate drinkers, including lower rates of cardiovascular disease and possibly fewer colds, Murray said.
"We always counsel people to avoid drinking to excess, but moderate drinking is not something that's very dangerous," he said.
As for marijuana, whose legalization for medical uses has been a matter of strong public policy debate for years, there is ample evidence that beneficial compounds can be found in the plant.
"Researchers are working around the clock to try to identify the ingredients in marijuana that have potential," to benefit human health, Baler said.
Once such chemicals are in a pure form, and researchers understand their effects on the body, then they could be put in clinical trials for use in cancer, multiple sclerosis, diabetes, glaucoma and other diseases, he said.
"There are segments of the population that want to bypass the entire process, grabbing this nugget of truth … and claiming smoking marijuana can be good for your health and have medical uses," Baler said.
Although for palliative care, he said, "that would be a different realm of medicine," in which the goal is to drug a person so they do not feel pain.
The year 2014 has brought with it the first legal sales of marijuana to people who aren't using the drug for medical reasons in the United States since the 1930s, as voters in Colorado and Washington state brought about this policy change.
Public health researchers have said studying rates of injuries, accidents, mental illness and teen use in the wake of the new laws will lead to a better understanding of marijuana's public health effects.
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