On Tuesday, the 31-year-old actor shared a lengthy post on Instagram alongside a photo of herself breastfeeding her six-month-old daughter Banks.
Duff welcomed her daughter with musician boyfriend Matthew Koma in October. She also has a son, Luca, who is six-years-old from a previous relationship.
In the social media caption, Duff explained that she was struggling to pump breastmilk while filming on the set of her TV show, Younger, and revealed how the stress of dropping milk supply made her feel as though she “was going to break”.
“Last week was my last week nursing Banks (my six-month-old),” Duff wrote.
“I am a working mum of two. My goal was to get my little girl to six months and then decide if I (and her of course) wanted to keep going.”
Duff went on to explain how “pumping at work sucks” revealing she had zero downtime and was usually forced to pump while getting her hair and make-up done for the next scene.
“Even if I had the luxury to be in my own room, it’s not even considered a ‘break’ because you have to sit upright for the milk to flow into the bottles!” she continued.
“Plus you are having your damn nipples tugged at by an aggressive machine that makes an annoying sound, that echoes through your head day and night (I swear that machine and I had many conversations at midnight and 3 am)!”
Duff also revealed how pumping led to a “drastic” fall in the amount of milk she was producing and that she lost “contact and connection” with her baby, leading her to feel “like a failure”.
“I was going to break. With the stress of a dropping milk supply and a baby that was getting bored or not caring about nursing when I was available to," Duff wrote.
“I was sad and frustrated and feeling like a failure all of the time. When really I’m a bad ass rock star. Mums get high on feeling like superwoman…because we are!”
Continuing to discuss the topic in the comments section of her post, Duff said she wanted to share her experience in case it might help anyone else who felt like they were struggling.
“I cried many times and felt so depressed while weening. I wasn’t myself at all. Something scary was hovering over my brain and my heart…the part of me that I know is smart and rational,” she explained.
“The lows felt horrible. I was missing good time with my baby. But I was really missing that natural oxytocin high."
Duff said that despite feeling so down, she finally came "out the other side" and called on all parents to remember they are a "superhero" for all that they do.
“Love you all and hope this helps anyone struggling!”
Duffs Instagram post has since garnered more than 800,000 likes and received hundreds of comments from fans and fellow mothers praising her for being so honest.
“Made me cry reading this! You’re SPOT ON,” one person commented.
“I went through such similar emotions and had no idea weaning would feel so emotional and sad. But then, it’s also freedom and a new stage... thank you for talking about it!”
Another added: “I am crying real tears reading this!!!! I feel you!!! Cheers to you! If anyone hasn’t told you today. YOU’RE A GREAT MUM!!”
A third wrote: “THIS THIS THIS! This is so important for mums to hear! thank you!!!”
The 38-year-old, who plays Yara Greyjoy of the Iron Islands on the hit HBO show, captioned the post: “Just a tease and my actual life on set between whatever we actually were filming."
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