A U.S. study of the arthritis drug Kevzara was stopped Thursday after it was shown to be no better than a placebo in treating critically ill COVID-19 patients. Researchers were hoping that Kevzara would help treat the “cytokine storm” experienced by those who are severely ill and were on ventilators, high-flow oxygen or in intensive care units.

According to the The Wall Street Journal, Regeneron Pharmaceuticals and Sanofi, who were conducting the clinical trials, also reported that 80% of the Kevzara patients had side effects compared to 77% who received placebos. The companies said that studies would continue outside the U.S.

STAT News reported in April that researchers were hoping that the drug, which is used for autoimmune diseases like rheumatoid arthritis, could help ease the immune system’s overreaction to the virus. This overreaction is called a cytokine storm and causes inflammation in the lungs of some of the sickest COVID-19 patients.

An earlier article published in the Journal reported that the pharmaceutical companies shut down part of their study when Kevzara showed no benefit in hospitalized patients who were not on oxygen or ventilators to concentrate their efforts on treating only the severely ill.

Early data from a small Chinese study showed some promise that a similar drug, Actemra, could benefit the critically ill. However, the U.S. trial showed that in some patients, Kevzara worsened their condition and ultimately showed no benefits.