Woman Using Mounjaro Weight Loss Jab Reveals Unexpected Side Effect As Her Breasts Grew To 34NN

When Tianna Moon lost three stone while using Mounjaro, it initially felt like everything was falling into place. She had hoped to slim down her waist, but she never expected the medication to cause her breasts to grow even larger.

The 30-year-old explained that she had always had a larger chest, but after deciding in May 2024 to focus on weight loss, her breast size increased from an L cup to an M. That change meant her bust circumference grew by roughly an inch, despite the rest of her body getting smaller.

While the UK-based content creator found it strange that her breasts were growing as her weight dropped, she did not immediately realize something was wrong. It was only after reading health forums online and doing further research, including using ChatGPT, that she began to suspect there was a medical issue behind the changes.

Moon has since been diagnosed with gigantomastia, a rare condition that causes rapid and extreme growth of breast tissue. Since receiving the diagnosis, her chest has continued to grow, leaving her struggling to find bras that offer proper support or comfort.

The 30-year-old content creator went from an L cup to a ‘NN’SWNS

Moon says the condition has caused severe back pain and painful sores, but she has tried to adapt by buying the largest bras she can find and forcing herself to wear them.

That approach led to cuts and torn skin beneath her breasts, which eventually grew to a size 34NN as she lost a further two stone. She explained: “Bras are impossible. Bras in my size NN don’t exist.”

“I decided to lose weight and eventually started on Mounjaro and lost three stone over the course of a year. In that time my breasts grew from an L cup to an M cup.”

Because of the ongoing pain, Moon has since stopped wearing bras altogether, saying she feels more comfortable without them. More than six months after receiving her diagnosis in July 2025, she says she is still dealing with the daily challenges caused by her chest size.

“The side effects are like having numb arms quite a lot and having quite severe indentations on my shoulders,” Moon shared. “I have some light scarring under my breasts where bras have rubbed and ripped the skin open.”

“Also laying on my back is not something I can do for a long period of time as it restricts the amount of air flow I can get in”

After suffering a head injury in 2021 and losing her job, Moon turned to OnlyFans as a way to earn money, using the attention her L-cup chest already attracted at the time.

Moon said: “It got to the point where last September I was in Amsterdam for the Xbiz awards as I was nominated. I was walking around with another lady and she said, ‘don’t you realise those people are pointing at you and trying to get your attention?'”

“It’s become so normal to me I don’t notice it anymore”

Tianna is exploring the possibility of breast reduction surgerySWNS

When her weight dropped from 19 stone to 14 stone and her breast size increased by three cup sizes, Moon decided she needed medical answers. After learning about a milder condition involving breast tissue growth, she booked an appointment with her doctor.

She said: “Originally, he was looking at macromastia, 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’.”

“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.”

Moon says her breasts now weigh a combined three stone, which causes constant discomfort and ongoing back pain. In November, she took further steps to protect her health, paying for a gastric sleeve procedure to reduce the risk of even more strain on her body.

Although she is considering breast reduction surgery, the OnlyFans creator has seen a financial boost since developing gigantomastia, earning roughly $13,000 per month.

She said: “I might as well try and reap the benefits of my medical condition rather than the negatives.”

It was actually one of Moon’s subscribers who first pointed out that her chest appeared to be growing beyond what she realized herself. She added: “As they got bigger, it was actually a subscriber who said you need to get remeasured because you are not the size say you are.”

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