Research has suggested that people's mental view towards their treatment can influence its effectiveness.
Conducted by the University of Oxford, the study looked at MRI scans of patient's brains.
They found that people's brain pain networks responded to different extents after being given pain killers depending on the expectations of the volunteer.
When the patient had positive expectations, the natural physiological or biochemical effect of opiod drugs was doubled.
Professor Irene Tracey at the Centre for Functional Magnetic Resonance Imaging of the Brain, commented: "Doctor's shouldn't underestimate the significant influence that patients' negative expectations can have on outcome."
The team noted that doctors should take patients' mental outlook and negative experience into account when treating them.
Some people may have had a number of drugs that have done nothing for their chronic pain. As such, they are less likely to expect results from new drugs, and therefore could be less likely to receive them.