In an emotional letter posted on Twitter, the singer said she was "devastated" by the decision to leave the last two shows.
Adele performed 121 shows over the last 16 months and was set to close out her worldwide tour supporting her Grammy- winning "25" this weekend with two sold-out shows at London's Wembley Stadium.
"To not complete this milestone in my career is something I'm struggling to get my head around and I wish that I wasn't having to write this," she wrote.
The singer said she had been struggling vocally the last two nights, writing, "I had to push a lot harder than I normally do. I felt like I constantly had to clear my throat, especially my vocal cords."
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Adele was told by her doctor avoid performing her final shows today and tomorrow.
"But I've never done it and I cannot in a million years do that to you. It wouldn't be the real me up there.
"I'm sorry. I'm sorry for your disappointment. I'm sorry for the nights you would have had with your loved ones and the memories you would have made together. I'm sorry for the time and money you've spent organizing your trips. You know I would not make this decision lightly," she said.
Adele's fans, however, offered support to the singer, saying her health came first.