Rare condition explained as woman's boobs grew to 34NN despite five stone Mounjaro weight loss
A rare condition that causes boobs to grow excessively big has been explained after a woman complained her 34NN chest was having a severe impact on her health.
Tianna Moon, a 30-year-old woman from the UK, was left baffled when her boobs continued to grow after she set herself the mission of shedding some weight.
Tianna, who was left unable to work after a head injury, launched an OnlyFans career in 2021 and rakes in around £10k per month from the online sex site.
However, it was there she got some health advice that changed her life, after a subscriber pointed out that her boobs were bigger than she initially thought.
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She had sought out Mounjaro jabs in the hope of reaching a weight which would allow her to get breast reduction surgery, with the sheer size and weight of her chest causing her some health issues such as numb arms, ripped skin and reduced air flow when lying on her back.
Although she managed to lose 5kg on the popular weight loss drugs, she was shocked to discover that her breasts had grown from a L cup to an M cup, eventually seeking out medical advice due to the 'odd' situation.
She said: "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’.
"I got the diagnosis quite early because of the growth not being common with anything else. At that point, I decided to get rid of the extra weight and protect my back because of the diagnosis."
Tianna underwent a gastric sleeve privately in November 2025 to help 'protect' her back and 'prevent future pain', while she's also considered breast reduction surgery, but has been warned her boobs could well grow back to their current size.
What is gigantomastia?
Gigantomastia, which is also referred to as breast hypertrophy or macromastia, is a rare condition that involves developing extremely large boobs due to excessive breast tissue growth.
The rapid and disproportionate growth can happen during puberty or later in life and is characterised as a rare condition when the breasts have an excess of at least five pounds of breast tissue, or make up more than three percent of your total body weight.
According to Cleveland Clinic, only around 300 cases have been reported worldwide, which makes it an exceedingly rare condition that can cause both physical and emotional pain.
As well as neck, back and breast pain, bras can also cause issues as they leave itchy indentations on the skin, while some cases will also have infections, poor posture and a loss of feeling in the nipples.
It can also cause issues with breastfeeding, due to complications such as blisters and low milk supply.
Why does it occur?
Doctors have identified four different types of gigantomastia, including: juvenile gigantomastia (during puberty), gestational gigantomastia (during pregnancy), drug-induced gigantomastia and idiopathic gigantomastia (unknown causes).
Hormonal changes, autoimmune diseases such as lupus or arthritis, obesity or genetics have also been identified as potential contributing factors.
How can it be helped?
As Tianna discovered, there isn't an instant fix when it comes to the rare condition.
Although breast reduction surgery is touted as a potential option for anyone suffering from having excessively large breasts, there isn't a guarantee that they simply won't come back.
In severe or recurring cases, a mastectomy may also be offered to remove all breast tissue.
Some medications can also be utilised as a way of stopping or slowing the breast tissue growth, but this would be little solace for someone whose breasts are already at a painful point.
James Moorhouse