Video games rated “M” for mature audiences contain sexual content, drug references, and strong language not labeled on the box, according to a recent study by Kimberly M. Thompson, an associate professor of risk analysis and decision science at the Harvard School of Public Health.

Thompson has previously completed studies analyzing the content of video games rated “E” for everyone and “T” for teen. Those studies found much higher levels of violence than advertised on the video game box.

She has also founded KidsRisk, a project that looks at the many hazards children are exposed to—from bath tubs to vaccines.

Her most recent study, “Content and Ratings of Mature-Rated Video Games,” looked at a random sample taken from all M-rated games available for Xbox, Game Cube and Playstation 2.

The two top-selling games of 2004 were “Grand Theft Auto: San Andreas” and “Halo 2,” both rated “M,” according to the NPD Group, a market research firm.

“We found that [these] video games were correctly labeled with the violence and blood content,” said Thompson. “However, we are finding sexual content, substances, and language that is not listed on the box.”

For example, one game, “Twisted Metal: Black,” used the words “mother fucker,” “bitch,” and “piss,” but was not labeled as containing profanity, according to the study.

“Kids spend six hours a day consuming entertainment material,” Thompson said. “Parents need to be aware of actual content.”

Karen G. Tepichin, a Harvard Law School student and co-author of the study, spent months quantifying the content of video games second-by-second.

The inconsistency in labeling “really confuses parents and consumers in forming a judgment on how appropriate the game is,” Tepichin said.

Thompson said, “While we didn’t look at the effects [of video games with strong content], evidence suggests that exposure to violent media increases aggression.”

She hopes that pediatricians will take a more active role in asking patients about video games, and that parents will “talk to kids more about their experience with games.”

Thompson hopes to synthesize this work with her studies of movie ratings, and to eventually work towards a standardized system to assign ratings for multiple media.