A popular women’s health and fertility app sows doubt about birth control, features claims from medical advisers who are not licensed to practice in the US, and is funded and led by anti-abortion, anti-gay Catholic campaigners, a Guardian investigation has found.

The Femm app, which collects personal information about sex and menstruation from users, has been downloaded more than 400,000 times since its launch in 2015, according to developers. It has users in the US, the EU, Africa and Latin America, its operating company claims.

Two of the app’s medical advisers are not licensed to practice in the US and are also closely tied to a Catholic university in Santiago, Chile, where access to abortion remains severely restricted.

Femm receives much of its income from private donors including the Chiaroscuro Foundation, a charity backed almost exclusively by Sean Fieler, a wealthy Catholic hedge-funder based in New York.

Fieler’s foundation has long supported organizations – and politicians such as the vice-president, Mike Pence – that oppose birth control and abortion. Fieler has criticized Republicans for failing to outlaw abortion, calling their reticence “the tyranny of moderation” in a recent editorial.

The Chiaroscuro Foundation, with Fieler as its chairman and main backer, provided $1.79m to the developers of the Femm app over the last three years, according to IRS statements. Fieler also sits on the board of directors for the Femm Foundation, a not-for-profit which operates the app.

The Femm app does not readily disclose the philosophy of its funders or leaders, and markets itself as a way to “avoid or achieve pregnancy”.

Other fertility apps have been criticized for monetizing intimate data, sharing data with third parties and lack of privacy protections. Femm has not been accused of such behaviour, but appears to be the first ideologically aligned fertility app.

The Femm app’s literature sows doubt about the safety and efficacy of hormonal birth control, asserting that it may be deleterious to a woman’s health and that a safer, “natural” way for women to avoid pregnancy is to learn their cycles.

Dr Lindsay Rerko, a physician who is licensed to practice as a family doctor, not a gynecologist, features on Femm’s website and writes that the “side effect profiles” of hormonal birth control suggests “they are causing illness and degrading health”.

Part of the Femm app encourages women to visit its own network of physicians for hormone tests, which it claims can diagnose “underlying” medical disorders. In an interview with the Guardian, Rerko declined to comment on whether she opposes birth control or abortion.

In fact, 57% of all married or in-union women of reproductive age worldwide use a modern contraceptive method, including condoms, hormonal birth control and implantable devices such as intrauterine devices, according to the United Nations in 2015. In North America, 69.3% of partnered women of reproductive age use modern methods such as the pill, IUDs or implants.

Fertility awareness birth control methods, such as that promoted by Femm, are considered the least effective, resulting in roughly 24 pregnancies for every 100 women using the method a year, according to the Centers for Disease Control and Prevention (CDC). Implantable devices are considered the most effective, resulting in one pregnancy for every 2,000 women a year.

“The birth control pill is one of the greatest health achievements of the 20th century,” said Dr Nathaniel DeNicola, an OB-GYN with the American College of Obstetrics and Gynecology, which has studied fertility apps extensively. “This is part of standard women’s healthcare.”

“Natural” family planning methods using fertility awareness are known to have a failure rate of about 25 unintended pregnancies for every 100 women a year in the US.

Anna Halpine, CEO of the Femm Foundation, said the ideology of the group and its funders is irrelevant because the Femm app is “not dealing with the question of abortion in the work and the research and training we offer”.

“Femm has never commented on the abortion issue. And doesn’t work in that area. Femm is an organization committed to expanding information research and knowledge about women’s reproductive health around the world,” said Halpine.

The Reproductive Health Research Institute (RHRI) provides Femm’s medical assertions, research and training. The two physicians leading RHRI are listed on its website as Pilar Vigil and Patricio Contreras. Vigil is listed as the medical director of RHRI, which has two addresses, one in New York City and another in Santiago, Chile.

Vigil is listed as an OB-GYN and Contreras as a “medical doctor”, but neither is licensed to practice medicine in the United States. Vigil’s biography lists her postdoctoral studies at the Texas Institute for Reproductive Medicine and Endocrinology. That institute closed in 2016, and said on its website it is “not processing any more requests for records”.

When asked whether the medical advisers to the Femm app are licensed to practice medicine in New York or the United States, Halpine said: “No.” She added the advisers are primarily in Chile.

The institute is registered at the same New York City address as the Femm Foundation and another anti-abortion organization called World Youth Alliance. When the Guardian tried to call RHRI, a receptionist answered the phone as the World Youth Alliance.

Halpine founded World Youth Alliance and was listed as CEO on the group’s most recent tax filings. World Youth Alliance gave Femm $446,042 between 2016 and 2017. World Youth Alliance also received funding from Chiaroscuro Foundation.

In multiple papers published by Vigil, she is affiliated with the Vicerrectoría de Comunicaciones Pontificia of the Universidad Católica, Chile’s Catholic University. In one editorial, titled The Harmonious Relationship Between Faith and Science, Vigil examines the position of Catholic saints on science.

The Guardian contacted a co-author of one peer-reviewed paper promoted by Femm Foundation’s 2017 annual report. The co-author is listed as Santiago Molina, a Tallahassee, Florida, community college anatomy professor.

Molina said his main contributions were “pondering questions” and translation. A physician who reviewed the paper at the Guardian’s request said it “doesn’t really align with any standard of care we practice in the US”.

According to the Femm Foundation’s annual reports, it received $618,653 in donations in 2017. The same year, Chiaroscuro gave Femm $445,500, the majority of its budget. Chiaroscuro gave an additional $350,000 in 2016, and $1m in 2015.