The UK’s Advertising Standards Authority (ASA) has found a Facebook ad describing Natural Cycles as a "highly accurate contraceptive app" and a "clinically tested alternative to birth control methods" to be misleading after receiving three complaints about the paid-for post.

The Swedish company said it removed the ad, which ran for approximately four weeks in mid-2017, as soon as it was notified of the complaint, but the advertising watchdog warned it "must not appear again in the form complained about".

In its ruling, the ASA told the Stockholm-based firm "to take care not to exaggerate the efficacy of the app in preventing pregnancies."

Based on a monthly or yearly subscription, Natural Cycles, which has been CE marked in Europe and very recently cleared by the FDA as a medical device for contraception, can be used in combination with a basal thermometer and protection on fertile days.

Users have to take their temperature in the morning and manually enter the data, along with information about their cycle, and the app’s algorithm generates insights to let them know whether they need to use protection.

An independent expert fact sheet published by the Swedish firm said several clinical studies assessing the effectiveness of the app found it improved "the efficacy of traditional fertility awareness based methods." For its decision, the FDA cited clinical studies of 15,570 users who used the app for an average of eight months. In these, the Natural Cycles demonstrated a “perfect use” failure rate of 1.8 percent, implying that 18 women in 1,000 using app correctly for a year will become pregnant, and a “typical use” failure rate of of 6.5 percent for those occasionally using the app incorrectly, the agency said.

Last year, after the company raised $30 million in a Series B round led by EQT Ventures, nuclear physicist Dr. Elina Berglund, who founded the company with her husband Dr. Raoul Scherwitzl, told MobiHealthNews they could move to a "connected thermometer that could automatically upload data" in the future. 

A spokesperson for the firm said it respected the ASA’s ruling.

"We are committed to being open and transparent in our communications to ensure our message is clear and provides women with the information they need to determine if Natural Cycles is right for them. As part of these efforts, every advertisement undergoes a strict approval process," they said. "Natural Cycles has been independently evaluated and cleared by regulators in Europe and the US based on clinical evidence demonstrating its effectiveness as a method of contraception.”

However, this is not the first time the app has come under fire in Europe. 

The Swedish Medical Products Agency has been investigating Natural Cycles after it was revealed that a major hospital in Stockholm found 37 out of 668 female patients seeking an abortion during September and December last year had been using the app for birth control.