Drug side effects place a considerable burden on health care systems, clinicians and patients. For example, the annual costs associated with adverse drug-related events in the US rose from $76.6 billion to over $177.4 billion between 1995 and 2000 1. Side effects are generally defined as an action of a drug other than the one for which it is being used. They do not only include drug or drug-use induced adverse effects, but also side effects brought about by patient, treatment or doctor-related factors, such as beliefs and expectations. Most studies have focused on the incidence of relatively infrequent but medically serious adverse events, morbidity and mortality 2. However, the majority of side effects are non-serious and non-specific symptoms that are not clearly attributable to the pharmacologic action of a drug. Depending on the method of ascertainment and the patient population, they comprise 62% to 89% of all patient-reported adverse effects 3, 4. Non-specific symptoms that the patient perceives to be medication-related are frightening and distressing to patients, decrease quality of life 5, cause non-adherence 6, 7 and add to the cost of treatment. Such side effects are even seen in patients taking placebo rather than active drugs 8,9. Understanding the determinants of non-specific side effects would be particularly useful in managing patients with chronic diseases, as it may provide guidance in deciding whether to discontinue or adjust the dose of a medication and/or treat the symptom with another agent if the medication is viewed as medically essential. Side effects to placebo (the nocebo phenomenon) are widely reported. In randomized controlled trials of arthritis therapy, the incidence and type of many side effects are similar in patients taking active drugs compared to those taking placebo 10, 11. In addition, there is a clinical impression that some patients are more likely to report and suffer from bothersome effects than others. This suggests that patient characteristics along with disease and medication variables affect side effect reporting 12. Side effect reporting has been associated with patient’s expectations, prior experiences with medication, gender, age, anxiety, and depression 3, 8, 13. One reliable measure of patient’s positive and negative expectations regarding their medications is the Beliefs about Medicines Questionnaire (BMQ) 14. This questionnaire assesses an individual’s perceptions of medicines prescribed for them on the basis of how they judge their personal need for the medication (Necessity beliefs) relative to their concerns about potential risks (Concerns). In studies across a range of illnesses including asthma, diabetes, cancer 15, depression 16, 17, HIV/Aids 18, 19 and rheumatoid arthritis (RA) 20, 21, medication beliefs are more strongly associated with adherence than socio-demographic or clinical factors, with low adherence related to doubts about personal needs and concerns about side effects. Specific concerns include commonly-held beliefs about the potential dangers of regular medication use like dependence or accumulated long-term effects 14, 22, they are prevalent even among patients who have not experienced side effects from medicines 19. However, little is known about the direct relationship of medication beliefs and side effects. We hypothesized that patients with negative beliefs about their medications would report more side effects, and that the predictive value of those beliefs persists after taking into account objective measures of disease severity and the medication regimen. Furthermore we hypothesized that pre-existing beliefs about medicines would influence subsequent side effect reporting, as opposed to prior experience with side effects from arthritis medication generating negative beliefs about those medicines. A further aim was to determine whether beliefs about medicines have a specific effect on side effects when patients start with a newly prescribed drug. It was hypothesized that RA patients with heightened specific concerns about arthritis medications would experience more bothersome symptoms that they view to be caused by the new medication 23. We believe this to be the first investigation of the nature, direction and course of these relationships in RA patients. Understanding these factors can inform clinical practice. If negative beliefs precede increased side effects reporting, needless termination or adjustment of dose, or additional medications to mitigate these nocebo effects might be averted.