It is an article that appeared a couple of years ago in The Guardian titled "Placebo effect works even when patients know they are getting a scam drug". It tells of a group of irritable bowel syndrome patients who received a placebo while being fully aware that it was a placebo.
The article states that:
The second group was told by the doctors that they would be taking "placebo pills made of an inert substance, like sugar pills, that have been shown in clinical studies to produce significant improvement in IBS-symptoms through mind-body self-healing processes".
"Not only did we make it absolutely clear that these pills had no active ingredient and were made from inert substances, but we actually had 'placebo' printed on the bottle," said Kaptchuk. "We told the patients that they didn't have to even believe in the placebo effect. Just take the pills."
The results, published in the scientific journal PLoS ONE, showed that the placebo pills were more effective at relieving symptoms compared with doing nothing at all.
In the same newspaper, there is an opinion article written by Ed Halliwell which is also relevant--"Let's be honest about placebo".