The nocebo effect is the opposite of the better known placebo effect - Latin for 'I will harm' rather than 'I will please'. Just as dummy pills are known to produce beneficial results among around 25% of patients who believe them to be the real treatment, they also trigger side effects in many patients.
Interestingly for information designers, it's been suggested that lists of specific side effects in patient information leaflets (or web pages aimed at patients) may contribute to the effect.
And it turns out that the colour, size and shape of pills has long been known to influence their effectiveness: red, orange and yellow pills have a stimulant effect, while blue and green are more sedative. People expect pills for their heart to be red (but not necessarily heart-shaped, as far as I know).
Good reference on this is: Barsky et al (2002), Nonspecific medication side effects and the nocebo phenomenon. JAMA vol 287, 5, 622-627.