The broadcaster, 45, who co-hosts Great British Breakfast said her early-morning starts were exacerbating her symptoms.
She wrote on social media: “During the summer I discovered I have a tumour in the inner canal of my right ear.
“Thankfully it’s benign and not hugely detrimental to my normal life.
“However the tumour has caused severe tinnitus which makes it very difficult to sleep.
“Sadly my 3am starts at GB news, compounded by sleep deprivation, are exacerbating my symptoms.
“I’ve taken the difficult decision to step back from my role on the Great British Breakfast while I focus on my health.”
Ms Gallacher said GB News had been “incredibly supportive” and she looked forward to returning to her role as soon as possible.
“As I adjust to managing my condition, I will carry on my less disruptive work commitments and continue maintaining a healthy lifestyle and training so I can get back to my normal routine quickly,” she said.