Caitlyn Jenner has revealed she once considered suicide before coming out as a transgender woman.

The former Olympic champion said she hit rock bottom when a US gossip site published a photo of her emerging from a doctor's office after having her trachea shaved to look more like a woman.

"It got to the point where I thought, you know what, I know the easy way out. I got a gun in the house.

"But then the next day I thought, wouldn't that be the stupidest thing you've ever done, to silence your voice?

"You have the opportunity here to really make a difference, to live your life honestly."

Jenner, who first revealed she had transitioned to a woman two years ago, was speaking as she promoted her new memoir The Secrets Of My Life.

She said: "I needed to pour my heart out on everything.

"What I was trying to accomplish is, one, get it all out for myself, so there was no other secrets left, but two, it was the way I dealt with my stuff."

Jenner also revealed she had a false start in transitioning in the 1980s.

She took hormones, then stopped, but her enlarged breasts did not disappear after the treatments stopped, requiring liposuction as she continued living as a man.

The book is dedicated to Jenner's late brother and father.

She said if her father had known "it would have been very difficult for him, just like it would be difficult for me".

The reality TV star said she is now "extraordinarily comfortable" with herself.