A lesbian Mormon teenager has written a book about being held in captivity for eight months and tortured in order to try to make her straight.

Alex Cooper, now 21, came out aged 15 to her Mormon parents, back in 2009.

After initially throwing her out of the house, her parents decided they would attempt to “fix” her sexuality.

Sent to the home of fellow Mormons Tiana and Johnny Siale, Utah, the teenager was made to wear a backpack full of stones for 18 hours a day.

Her story is set out in her new book ‘Saving Alex’, which explains that the couple she was sent to live with didn’t have any professional counselling experience or training.

The stones trick was apparently an attempt to make her “feel the burden she was carrying by choosing to be gay.”

Naturally, Cooper was “angry”, and “determined to find a way out”.

The couple told her: “Your family doesn’t want you. God has no place for people like you in His plan.”

After attempting suicide and trying repeatedly to escape, the couple tried to beat her, writes Cooper.

According to the author, various visitors knew about the abuse, but nobody tried to stop it from happening.

The teenager was eventually allowed to attend high school where she joined the gay-straight alliance, and was introduced to an attorney who helped her get a court order protecting her from being forced into “conversion” therapy.

“I think that’s what a lot of parents are under the impression of, that they’re doing the best thing for their child,” the author told The Salt Lake Tribune.

“I don’t blame my parents,” she told KUTV. “I am able to share my life with them, and it’s awesome.”

The 21-year-old is now no longer a practicing Mormon, and did not prosecute the Siales for their actions.

The Church of the Latter Day Saints no longer advocates for “conversion” therapies, but it does teach that being gay is a sin, and in November barred the children of same-sex couples from being baptised.