SAN DIEGO — Researchers gave San Diego smokers cigarette packs with graphic warning labels to see whether they discouraged smoking, and the gruesome pictures made participants more likely to hide their habit than actually cut back.

The study, conducted by a group of public health experts led by UC San Diego, gave packs to 357 local smokers who agreed to purchase their preferred brand through a study website. They got the same cigarettes they always smoke, but the product they received didn’t necessarily look the way they’re used to.

Some participants got blank packs or cigarettes with the standard commercial wrapping. But others got packs covered in graphic warnings — some of them gruesome, like a close-up of a person’s foot with a bad case of gangrene.

According to a news release sharing the results of the study Thursday, participants with the graphic packs “continued to smoke as often as they did before and after the study.”

The most noticeable change in behavior was how openly the participants displayed their habit. The smokers hid their packs 38% more often than they normally would, according to the researchers. That behavior returned to normal when they got back their regular packs.

These examples of graphic warning labels, pulled with permission from the Australian government, include a grotesque depiction of gangrene and a photo of man who had a throat procedure. (Photo: UC San Diego)

“Prior to the study, we found that many smokers in the U.S. were discrete and reported hiding their usual pack in public settings. The packs with graphic warning labels had their main effect on those who were least likely to hide their packs prior to the study,” senior author David R. Strong said in a statement. “We found no evidence that graphic warning-labeled packs changed smoking behavior over the year-long study.”

But the researchers said that regardless of how it affected existing smokers, making cigarette packs less socially acceptable in general — as the labels appeared to do — could have an affect on people picking up the habit.

“We demonstrated that smokers in the U.S. who received cigarettes in packs with graphic warning labels were less willing to display the packs in public. It has been hypothesized that this behavior could reduce perceptions by teens that it is socially acceptable to smoke, perhaps explaining why mandated graphic warning label packs are associated with reductions in teen smoking,” first author John P. Pierce said in a statement.

While the unsightly warnings are a mostly foreign concept to smokers in the U.S., graphic packaging is already mandated in more than 120 countries. Congress approved similar requirements in the U.S. back in 2009, but the labels have been held up by repeated legal challenges.

Read more about the study and its methodology here.