A survey by Consumer New Zealand and the Council of Medical Colleges found that patients feel uncomfortable about asking if treatment or tests are necessary.
According to the survey, 21 percent of people felt that doctors had recommended a test or treatment they didn't need.
Out of those, 24 percent went ahead and had the treatment - while 18 percent ignored the doctors suggestion.
"People should feel able to question health care treatment options," Consumer New Zealand chief executive Sue Chetwin said.
"There is mounting evidence that more tests and procedures did not always equal better care," Choosing Wisely medical director Dr Derek Sherwood said.
The survey was carried out as part of the organisations’ Choosing Wisely campaign, encouraging conversations about medical testing and treatment options.