The study involved patients with a particular kind of arthritis. While more research has to be done in patients with other illnesses to know for sure, "my guess would be that this is happening across a wide range of drugs," Dr. Yvonne Nestoriuc of Philipps-University Marburg in Germany, the study's lead author, told Reuters Health. "This is really something that happens in a lot of patient populations."

While most medication side effects are not life threatening or seriously harmful, she and her colleagues note in the journal Arthritis Care & Research, they can still be "frightening and distressing" to patients, and can also lead to patients not taking drugs as recommended.

People with a variety of illnesses who don't feel their medications are necessary and are concerned about their side effects are known to be less likely to take these drugs as directed, the researchers add.

To investigate whether these beliefs might be related to experiencing side effects as well, Nestoriuc and her team had 100 rheumatoid arthritis patients complete the Beliefs about Medicines Questionnaire, which explores general and specific beliefs about the necessity and risks of medication. Patients also reported on any side effects related to their rheumatoid arthritis medication and on how much they were bothered by these symptoms.

Rheumatoid arthritis is an autoimmune disease characterized by inflammation that leads to stiff, swollen and painful joints. It affects some 20 million people, according to the National Rheumatoid Arthritis Society.

At the study's outset, 77 of the patients reported having been bothered by side effects. Eighty-seven of the original 100 study participants were followed up at six months; 45 of these patients, or 52 percent, reported being bothered by side effects at this point.

The patients who had concerns about their medications, for example agreeing with the statement that "having to take arthritis medications worries me," were more likely to have reported having side effects, both at the study's outset and if they started a new drug during the six-month study period. Side effects typically included rashes, gastrointestinal discomfort, and headaches.

These patients were also more likely to report these side effects to their doctors, take non-prescription medications to deal with them, and change their medication dosages on their own. The only other factor that influenced the likelihood of reporting side effects was age.

Patients with rheumatoid arthritis "who are especially concerned about their arthritis medications, or who expect side effects, are at greater risk of experiencing them," the researchers say.

"Starting a new drug is a specifically risky time because people tend to misattribute pre-existing bothersome but nonharmful symptoms as side effects of the new drug," Nestoriuc said.

Doctors may be able to help their patients avoid side effects by talking with them about their concerns before prescribing a new medication, she added, and helping them to get a more "realistic view about the drugs."