Obesity is a large problem in the U.S., but some think a small warning label could fight it.

San Francisco is trying to curb obesity by requiring all public soda advertisements on buses and billboards to have warnings about the harmful health effects of drinking soda.

This is the second time California has attempted to put warning labels on soda. The first attempt failed to pass from a state senate committee in 2014.

Yet, studies show that these typical warning labels aren’t working.

“Warnings appear on everything from video games to alcohol and cigarette labels, but do they actually change behaviors?” Martina Cartwright reported for Psychology Today. “Historically, warning labels on controlled substances like alcohol and tobacco increase consumer awareness but studies are mixed as to their impact on behaviors.”

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An Australian study shows that warning labels on alcohol don’t keep adolescents from drinking, Cartwright reported.

This same trend applies to warning labels on sodas, especially warning labels on advertisements, Tom Jacobs reported for Pacific Standard.

“The warning labels effectively set up a battle between words and images,” Jacobs wrote. “And in this study, at least, images were powerful enough to counterbalance the effect of the warnings.”

The U.S. has required warning labels, small boxes with text only, to be printed on cigarette packaging since 1965. However, the minimal labels are shown to be less effective at informing smokers of the health effects and deterring smoking than other countries’ more graphic-oriented labels, the Harvard School of Public Health reported.

The Food and Drug Administration proposed a series of new warning labels, which were more graphic and intense. However, they were shut down by an appeals court in 2013 because the large labels infringed upon cigarette companies’ first amendment rights, CBS reported.

One possible reason warning labels are failing stems from advertising. Telling consumers that smoking or drinking can cause health problems is hard to reconcile with advertisements that make these behaviors seem fun and appealing.

Countless studies have shown the inextricable link that exists between alcohol advertising and underage drinking. A 2013 study linked increased alcohol advertising exposure to underage drinking, missing school and getting in fights, Perri Klass reported for The New York Times.

In addition to typical forms of advertising, Klass warns of social media marketing, which encourages potential customers to like or follow brands, and suggests parents talk to their children about the dangers of advertising and other negative media messsaging.

“Know what your children are watching,” Klass wrote. “Watch with them. Talk about what you see — the images on billboards or on touchscreens, the Super Bowl commercials, the Web sites they visit.”

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Shelby Slade is a writer for Deseret News National. Email: sslade@deseretdigital.com, Twitter: shelbygslade.