Turn on, tune in, have babies.

The tide of medical-marijuana legalization making its way through American states is leading to a notable uptick in the birth of babies, according to a new paper published by the National Bureau for Economic Research.

According to the National Conference of State Legislatures, 33 states and Washington, D.C., allow the once verboten drug to be used for various health-related reasons. And in these states, the researchers—Michele Baggio and David Simon of the University of Connecticut and Alberto Chong of Georgia State University—found an uptick in marijuana use.

And when more people smoke marijuana, they get friskier and, apparently, more careless. After legalization, there’s “increased frequency of sexual intercourse, decreased purchase of condoms and suggestive evidence on decreased condom use during sex,” the authors wrote in the paper.

“In the specific case of marijuana, it is typically believed that its consumption heightens sensory perception, increases relaxation, reduces stress and diminishes anxiety,” the paper says. “A feeling of relaxation may change attitudes toward taking sexual risks by becoming less concerned about the consequences of sexual intercourse, including reducing protection or taking on more sexual partners.”

The result is a baby boomlet.

“We find that the enactment of any medical marijuana laws increases the birth rate by 0.40 or approximately 4 births per quarter for every 10,000 women of childbearing age,” the paper said. “These results provide evidence that marijuana use has a considerable, unintended, and positive effect on fertility.”

The U.S. general fertility rate in 2017 was 60.3 births per 1,000 women aged 15 years to 44 years, down from 62.0% in 2016, according to the Centers for Disease Control and Prevention.

The authors looked at data from 2004 through 2014. They drilled down to county-level condom sales, although the paper does not consider how other forms of birth control might have influenced their findings.

Kasey Buckles, a University of Notre Dame economics professor who studies demographics and family issues, said the paper does indeed suggest “a large effect” on births tied to medical marijuana laws. The paper indicates that “if we went from marijuana being illegal everywhere in the U.S. to being legal everywhere, you would get about 120,000 more births per year, as there are roughly 4 million births each year in the U.S.,” Ms. Buckles said.

In an interview, Mr. Chong noted that any uptick in births comes in a climate where overall U.S. fertility rates have been under pressure. The general U.S. fertility rate has declined every year but one since 2007.

But he and his coauthors don’t believe that full legalization of marijuana will much affect the overall trend of this key demographic measure.

Others agree. Brad Wilcox of the National Marriage Project, a nonpartisan effort at the University of Virginia, said the research finds “a modest effect at the margin.” But he added, “I don’t see the legalization of marijuana as a silver bullet in pushing fertility rates up.”

Corrections & Amplifications

A previous version of this post misspelled Kasey Buckles’s first name. (Nov. 19, 2018)


U.S. Births Hit Lowest Number Since 1987 (May 17)

Cannabis Comes to Your Coffee and Candy—But Is It Legal? (Sept. 12)

Marijuana Makes for Slackers? Now There’s Evidence (Sept. 15, 2016)