Woman Says Her Breasts Grew Rapidly After Taking Mounjaro Weight-Loss Jab

A 30-year-old British woman, Tianna Moon, has opened up about the difficulties she faces after experiencing rapid breast growth while using the weight-loss drug Mounjaro.

Tianna, who lives in East Anglia, said her breast size increased from an L cup to NN and eventually to a 32OO, leaving her struggling with everyday activities including walking up stairs, sleeping and travelling for extended periods.

She has a rare condition known as gigantomastia, which causes excessive and sometimes rapid growth of breast tissue.

Tianna claimed she noticed significant changes in recent months while losing weight and using Mounjaro, although she did not establish that the medication itself caused the breast growth.

According to her, the size and weight of her breasts have made hot weather particularly uncomfortable.

“My boobs are like a heat factory and there isn’t really much I can do to keep cool.”

She said navigating stairs has also become increasingly difficult because her chest obstructs her view of her feet.

“Stairs are also a huge problem now. I’m forever tripping up on them. I have to go really slow, as I can’t see my feet anymore.”

Tianna said the condition has also affected her sleep. She claimed that after losing weight, she moves more frequently while sleeping and sometimes ends up lying on her back, causing the weight on her chest to make breathing uncomfortable.

“Sleeping is also something I’m really struggling with. Since losing weight, it’s easier for me to move in my sleep, meaning I end up on my back more.

“But I keep waking up frequently, as the added weight on my chest suffocates me.”

Despite attracting attention because of the unusual size of her breasts, Tianna said she is more concerned about the physical discomfort and pain associated with the condition.

She explained that undergoing breast reduction surgery may not provide a permanent solution because the glandular tissue could continue growing.

“I’m not the biggest in the world, nor do I want to be. I’m in so much pain now. A breast reduction isn’t a cure.”

Tianna also expressed concerns about potential complications from surgery, claiming that thinning skin around her breasts could make an operation more difficult.

She previously underwent gastric sleeve surgery in November 2025 as part of efforts to lose weight, but said the size of her breasts continued to increase.

She has since incorporated weight and resistance-band training into her routine to strengthen her back and improve her posture.

Tianna said the condition now affects several aspects of her daily life, including accidentally knocking objects over because of her limited downward visibility and experiencing upper-back pain when sitting in a car for more than an hour.

The difficulties have become particularly pronounced in recent months, she said, resulting in her spending much of her time at home.

While Tianna has associated the timing of the rapid growth with her weight-loss journey, gigantomastia can have different underlying causes, and her account does not establish Mounjaro as the cause of the condition.