Failure to take the drugs correctly reduces their effectiveness and may lead to a worsening of symptoms, warned researchers from the University of Manchester.
Rheumatoid arthritis develops when your immune system begins to attack itself, and symptoms include inflammation, pain and swelling in the joints and internal organs.
Not taking meds as prescribed
The study included 286 patients who had rheumatoid arthritis for seven years and had been prescribed anti-TNF drugs, which cost about $13,000 to $20,000 a year per patient. Anti-TNF drugs include etanercept (Enbrel), adalimumab (Humira) and golimumab (Simponi).
Twenty-seven percent of the patients said they didn't take the medications as directed at least once over the first six months after being prescribed the drugs, according to the study published recently in the journal Rheumatology.
Read: Treatment of rheumatoid arthritis
It's not clear whether the patients' failure to take the drugs as prescribed was deliberate or accidental, and further research is needed to learn more about why this occurs, the researchers said.
"If patients do not take their medication as prescribed it is likely to have a significant effect on whether they respond to therapy and could mean that their condition deteriorates more quickly, affecting their quality of life," study author and rheumatology expert Dr. Kimme Hyrich said in a university news release. "Non-adherence is also a waste of scarce health care resources and something that needs to be addressed."
Anti-TNF drugs changes lives
Anti-TNF drugs have transformed the lives of many patients with rheumatoid arthritis and related disorders, Alan Silman, medical director of Arthritis Research UK, said in the news release.
Read: Causes of rheumatoid arthritis
"This success has been at a considerable cost to the [National Health Service] but there was always the assumption that patients prescribed these drugs will have the necessary regular injections," Silman said.
"The fact that a considerable proportion of patients are missing doses of these very expensive agents is worrying, as clearly their effectiveness would be reduced," he added.
Smoking associated with rheumatoid arthritis
Drinkers are less likely to develop arthritis