When laws hold adults responsible when kids drink on their property, kids are less likely to spend their weekends drinking at parties, according to a new study.

States or local governments can enact ‘social host’ laws, which penalize adults hosting underage drinking parties with fines or imprisonment, potentially even if the adults do not furnish the alcohol.

Past research on the effectiveness of such laws has been limited, the authors of the new study write.

Social host laws may not be well enforced in many communities, and it is also likely that many parents and adults are not aware of the laws, which makes the new results somewhat surprising, said lead author Mallie J. Paschall of the Prevention Research Center in Oakland, California.

California has no statewide social host laws, but at least 75 cities and a number of counties have enacted them, he told Reuters Health by email.

For the new study, Paschall and his coauthors examined drinking patterns in 50 California cities with populations between 50,000 and 500,000 people, using city ordinances to rate the presence and strictness of social host laws.

The researchers contacted families with teens between age 13 and 16 in 2009 by mail and phone, and interviewed consenting teens by phone about their drinking habits.

The researchers called the same teens again to re-administer the survey in 2010 and a third time in 2012.

In the end, about 30 teens represented each city.

In 2009, 20 percent of the teens said they’d had a drink in the past year, which increased to 30 percent in 2010 and 44.5 percent in 2012, as the teens got older.

For specifically drinking alcohol at parties, 15 percent answered yes in 2009, which increased to 25 percent and 35 percent one and three years later, according to results in the Journal of Studies on Alcohol and Drugs.

The researchers found that social host laws were not associated with past year drinking or alcohol use behaviors.

In communities where adults reported more drinking, more kids tended to report heavy drinking over the past year, and cities with more bars per square mile also had more teens who reported drinking at parties.

However, kids who reported drinking over the past year were less likely to report drinking at parties in communities with stronger social host laws, the authors write.

In cities with the strictest social host laws, teens were 20 percent less likely to drink at parties compared to teens in cities with no social host laws.

“The laws make it costly to host parties or for young people to drink in each other's homes,” said Angela K. Dills of the department of Economics at Providence College in Rhode Island, who was not involved in the study. “Raising the cost of drinking tends to reduce alcohol consumption.”

Since these laws can vary, it would be useful to see which aspect is most effective: the specific focus on underage parties, its civil or criminal nature, the property types covered, and whether the property owner is required to have knowledge of the event, she told Reuters Health by email.

Since this study only identifies an association, it is possible that the laws themselves are not causing teens to reduce their partying, Paschall said.

“For example, it’s possible that those communities have more conservative norms regarding alcohol use, so teens in those communities were already drinking less before the social host laws were enacted,” he said.

He and his team are seeking National Institutes of Health funding for another study that would examine this question, he said.

“We still don’t really know how effective these laws are in preventing or reducing underage drinking and related problems,” Paschall said. “However, we do know that teenagers get alcohol primarily from social sources and very often in private settings.”

“So this may be an effective strategy for reducing the social availability of alcohol, along with laws such as keg registration requirements,” he said.