When Tianna Moon began taking the weight-loss injection Mounjaro, she expected a smaller body and a healthier future. Instead, she says, one part of her body grew at a terrifying pace.

The model from East Anglia already had an unusually large chest, wearing an L-cup bra. Within months of starting the so-called “skinny jab,” she says her breasts surged to an NN cup and then to a 32OO, a size that now leaves her struggling to walk, sleep and even see her own feet.

“The hot weather has been far from pleasant,” Tianna said. “My boobs are like a heat factory and there isn’t really much I can do to keep cool.”

Simple tasks have become daily hazards. Stairs are a particular nightmare. “I’m forever tripping up on them. I have to go really slow, as I can’t see my feet anymore. It’s ridiculous – but it’s the truth.”

Nights offer little relief. Since losing weight elsewhere on her body, she moves more in her sleep and often ends up on her back. “I keep waking up frequently, as the added weight on my chest suffocates me,” she said.

Tianna, 30, has been diagnosed with gigantomastia, a rare condition that causes rapid, excessive breast growth. While the dramatic change has pushed her into the spotlight as the woman with Britain’s biggest boobs, she insists the “title” means nothing compared with the pain.

“I’m not the biggest in the world, nor do I want to be,” she said. “I’m in so much pain now.”

Breast reduction surgery, often seen as the obvious solution, is not straightforward in her case. Gigantomastia can cause breast tissue to keep growing even after an operation. “The glandular tissue could continue to grow after a reduction and then I’d have scar tissue to factor in, too,” she explained. Thinning skin at the sides of her breasts also raises the risk of wounds tearing open. “Nobody knows why I have this condition and so it’d be hard to find a surgeon that would be happy to operate.”

Tianna underwent gastric sleeve surgery in a bid to lose weight, but her chest continued to expand. Now she relies on weight training and resistance bands to strengthen her spine and improve posture, trying to manage the strain of carrying her breasts.

“I forget how big my boobs are, as I live with them,” she said. “I’m forever knocking stuff over and walking into things since I can’t see.” Even car journeys longer than an hour leave her upper back in agony. In recent months, she has largely stayed at home, hoping for medical answers – and, above all, some measure of comfort.