Otago researchers say they've "unequivocally proved" that ME, also known as chronic fatigue syndrome, is a genuine illness.
The invisible illness affects more than 20,000 New Zealanders but sufferers often have the stigma of not having a "real disease" with symptoms "all in their head".
Warren Tate from Otago University's biochemistry department started researching the disease after his previously-vibrant daughter went rapidly downhill after a bout of glandular fever.
"I was absolutely convinced that there was a biological basis to the disease, it wasn't psychological or psychosomatic," Prof Tate told Newshub.
ME is triggered by a viral illness, changing the way the immune system responds. It causes long-term symptoms including a lack of energy, pain, and hypersensitivity to light and sound.
Prof Tate's research found patients have major changes in their physiology including lower metabolism and neurological symptoms.
"Unfortunately it doesn't provide the magic bullet which will provide a cure for you - they're very gracious in saying: 'We're just happy that you're actually working to understand our disease.'"
For sufferers, Prof Tate's research is about validating the disease. Rugby league star Richie Barnett struggled with the illness for 12 years from late in his sporting career and told Newshub no-one had the tools to help him.
"There was no help, there was no cure for it, there was no blood test.
"The doctors were not geared up to understand what that was like, to give you the tools and the ability to manage it better."
Barnett said he's felt better for the past four years, but for 95 percent of patients, it's a lifelong battle.
However, Tate believes the disease is reversible, and now researchers are focussed on finding the triggers that will force the healing process to begin for sufferers.