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The Love Island star, 30, said she used the Natural Cycles form of contraception to her 1.9 million followers.
In a lengthy sponsored post for the brand, Olivia said: "When I was younger I tried so many pills. For me it was awful, I had mood swings, migraines. I tried other options as well but found it uncomfortable. So, when I found @naturalcycles I was like - oh my God, this is like the golden ticket.
"I can avoid unplanned pregnancy, I can track my cycles and I don't have to put anything foreign into my body, it's amazing!"
However, fans raced to criticise the TOWIE star for promoting a form of contraception that has previously been branded as unreliable.
"What a risky thing to advertise to a younger audience," one follower wrote.
A second laughingly asked: "How much were you paid to promote this?"
"I actually love your all your posts and along with others disappointed you're promoting this," a third said. "Unfollowing."
"Be expecting a new arrival in a few series time then," a fourth sniped. "I swear I saw another person advertising this on here yesterday. Really irresponsible when you have impressionable you girls who follow you."
Olivia is the latest influencer to have been promoting Natural Cycles on Instagram.
Fellow Love Island stars Laura Anderson, Cara Delahoyde and Montana Brown have shared photos posing alongside thermometers.
Lucy Mecklenburgh also promoted the brand, shortly after partner Ryan Thomas said that none of his children had been planned.
Natural Cycles claims to be 93 per cent effective with typical use and 98 per cent effective with perfect use, and is hailed as the world's digital contraceptive.
However, as its algorithm calculates your fertility based on your temperature, which can be higher or lower for a myriad of different factors, it can lead to unwanted pregnancies. It also does not cater for fairly common ailments such as polycystic ovary syndrome, which can make your cycles irregular.
In Sweden, where the company is based, a major hospital reported that 37 of the 668 women who had sought an abortion there between September and December 2017 were using Natural Cycles as their sole form of birth control, according to The Guardian.
If you're thinking about switching away from your regular contraception, be sure to seek medical advice first.
Tyla has contacted Olivia Attwood for comment.
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