Dr Hoebel said he believed high-fat foods stimulate opioids or 'pleasure chemicals' in the brain.

BBC: Fast food 'as addictive as heroin'

Mike Bennett, St Gemma's professor of palliative medicine at the University of Leeds, said both doctors and patients needed reassurance about opioids.

BBC: Morphine and pain control

It is thought that a build up of chemicals like dopamine suppresses the activity of the brain's natural painkillers - the endogenous opioids.

BBC: Gene controls pain threshold

The hypothalamus also has connections to the cortex via the striatum and the nucleus accumbens, a structure that secretes its own dopamine and opioids in response to food (see graphic).

FORBES: Food on the Brain

Both are cancer patients but opioids are equally needed to help patients with a range of other debilitating conditions such as heart failure, kidney and respiratory illness and neurodegenerative disorders.

BBC: Morphine and pain control

Triptans, opioids, ergots or combination analgesic medications on 10 days a month or more or paracetamol, aspirin or an NSAID (anti-inflammatory such as ibuprofen) on 15 days a month or more.

BBC: Headaches and painkillers

Estimated hospitalizations for poisoning by prescription opioids, sedatives and tranquilizers increased 65 percent from 1999 to 2006, according to a study in the May edition of the American Journal of Preventive Medicine.

CNN: How physicians try to prevent 'doctor shopping'

While I go back and forth, I tend to agree that once you get beyond the short term release of endogenous opioids in response to the expectation of pain relief, a mysterious placebo effect that produces all sorts of miraculous effects is far less proven than people think.

FORBES: Harvard Placebo Study Was Seriously Overhyped