Woman’s 39-Lb. Breasts Won’t Stop Growing Due to a Rare Condition

Woman’s 39-Lb. Breasts Won’t Stop Growing Due to a Rare Condition — Which She Discovered While on Mounjaro

Woman’s 39-Lb. Breasts Won’t Stop Growing Due to a Rare Condition — Which She Discovered While on Mounjaro

Tianna Moon, 30, realized something was wrong when she lost weight but her breasts continued to increase in size

Toria Sheffield

Sat, February 7, 2026 at 11:00 AM UTC

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Tianna Moon. Tianna Moon / SWNS — Tianna Moon.
Tianna Moon / SWNS

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A woman was diagnosed with gigantomastia, a rare condition that causes her breasts to grow rapidly
Tianna Moon, 30, realized something was wrong when she lost weight on Mounjaro, but her breasts continued to increase in size
She has considered breast reduction surgery but said there’s “no guarantee" her breast tissue won’t grow back at the same rate

A woman was diagnosed with a rare condition that causes her breasts to grow rapidly — and she learned she suffered from the health ordeal thanks to a popular GLP-1 drug.

Tianna Moon of East Anglia, a region in eastern England, received her gigantomastia diagnosis in July, according to SWNS.

The 30-year-old, who has had larger-than-average breasts since puberty, first realized something was abnormal with her chest after she began using Mounjaro in 2024. (Mounjaro is an FDA-approved prescription medication for people with type 2 diabetes. It's a brand name for tirzepatide — also known as Zepbound — which is highly effective for weight loss by reducing appetite, increasing feelings of fullness and improving how the body breaks down sugar and fat.)

Losing weight while her breasts continued to grow, Moon's doctor eventually diagnosed her with gigantomastia, which causes breast tissue to grow rapidly and in excess, per the Cleveland Clinic.

Moon said her doctor "originally" considered she could be dealing with macromastia, a less severe but similar condition.

"But when I broke down medical history, the weight loss on Mounjaro and the increased growth and side effects, he was point-blank like, 'This is gigantomastia,’ " she recalled.

The condition can be caused by a variety of factors, including hormonal changes, genetics and autoimmune disorders, according to the Cleveland Clinic.

There are currently only about 300 reported cases of gigantomastia worldwide, the organization said.

Moon said her breasts currently weigh about 39 lbs. — which is approximately 20% of her overall body weight.

Tianna Moon after weight loss Tianna Moon / SWNS — Tianna Moon after weight loss
Tianna Moon / SWNS

And while she admitted her large breasts are “normal” at this point in her life, Moon said the rare condition still comes with challenges.

“The side effects are having numb arms quite a lot and having quite severe indentations on my shoulders,” she said.

Moon added, "I have some light scarring under my breasts where bras have rubbed and ripped the skin open.”

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“Also laying on my back is not something I can do for a long period of time, as it restricts the amount of airflow I can get in,” Moon continued.

When she goes out in public, Moon explained, "I try and make [my breasts] smaller than they are and strap them up. I [still] get stares and double takes."

Moon has considered breast reduction surgery, but she said there’s “no guarantee" her breast tissue won’t grow back at the same rate.

“People are telling me it’s disgusting I’m not having a reduction, and that I’m basically begging for attention,” she said.

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Moon has since established an OnlyFans account, opting to use her body challenge for financial gain.

“I might as well try and reap the benefits of my medical condition rather than the negatives," she said.

Moon added that her decision to create the account has helped her better appreciate her unique body type.

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