When Angelina Jolie published an essay in the New York Times about her decision in 2013 to get a double mastectomy, the essay quickly went viral.

Jolie’s frank and candid admission that she had inherited a “faulty” BRCA1 gene that increased her risk of developing breast and ovarian cancer and struggled with what to do struck a chord with people. Jolie revealed that she had undergone a medical procedure rarely talked about openly, much less by A-list celebrities, and said she hoped her experience could help others.

“Today it is possible to find out through a blood test whether you are highly susceptible to breast and ovarian cancer, and then take action,” Jolie wrote

A new study published in the British Medical Journal found that thousands of additional women got tested for mutations in the breast cancer risk genes in the U.S. — but probably not the right women.

Testing rates increased 64 percent in the three weeks after Jolie’s editorial, compared with the three weeks before, according to researchers at Harvard Medical School. The study can’t prove that Jolie’s essay caused the bump in testing, but researchers did not find a similar increase in test rates over the same time period the previous year. Meanwhile, the mastectomy rates among women who had a genetic test actually declined after the piece was published, suggesting the women who got the tests done weren’t as likely to have the mutation.

And all that testing comes at a cost: The researchers estimated 4,500 additional genetic tests were performed, at a cost of $13.5 million.

“The ‘Jolie effect’ is real,” said Timothy Caulfield, a professor of law at the University of Alberta who focuses on health policy and was not involved in the study. “One way to interpret that is that people who didn’t need to get the test got the test. That didn’t necessarily result in this targeted information campaign where people that were genuinely at increased risk and needed this test were getting this.”

The study suggests a double-edged sword when celebrities talk about health issues.

“Our findings suggest that celebrity endorsements can be extremely effective and relatively low-cost compared to a lot of public health awareness campaigns,” said Sunita Desai, a health care economist at Harvard Medical School who led the study. But they may not start the discussion among the people actually at greatest risk.

Jolie’s essay was a disclosure, not an endorsement — a window into her own decision-making when facing a scary prognosis. It was thoughtful and restrained and clearly noted that Jolie’s risks weren’t typical of most women who develop breast cancer.

“Only a fraction of breast cancers result from an inherited gene mutation,” she wrote. But the essay had a profound effect nonetheless, suggesting medical professionals may want to pay attention when celebrities talk about their own health. Actor Ben Stiller recently credited a prostate cancer screening test with saving his life, raising concerns that more men will get a form of screening that medical experts say causes more harm than good.

The downside of excessive testing may seem minimal. Maybe the women who got tested were unlikely to carry the gene mutation, but what’s the harm in knowing?

One answer is that the test cost, on average, $3,000. Unnecessary testing can waste limited health care resources and may also cause stress. But another way to answer the question is to think about the major causes of breast cancer in women. Most women who develop breast cancer never inherited a faulty BRCA gene; they develop cancer for other reasons. Learning a negative test result could possibly make them less cautious about other forms of prevention or screening.

“The negative effect of that disclosure is the women who went and had these tests, which came back negative now have a false sense of security that they weren’t going to develop breast cancer — which is totally wrong, because they still have the one-in-eight population” risk of the general public, said Mark Boguski, a pathologist who works at the company Inspirata and co-writes books about what people can learn from celebrity illness.