With recent deaths in an RA clinical trial, some are wondering about the safety of JAK inhibitors.

Last month, AbbVie reported two patient deaths during a late-stage clinical trial for arthritis drug upadacitinib.

The pharmaceutical company said the deaths were unrelated to the trial and weren’t linked to the drug — a once-daily pill for treating rheumatoid arthritis (RA).

AbbVie also says the study met its goals, and they are continuing with the drug as planned.

They tout upadacitinib as potentially the best RA medication in its class.

Upadacitinib is a JAK inhibitor, also known as a Janus-kinase inhibitor.

These drugs can be effective in the management of RA symptoms but also carry with them various side effects and risks.

However, often the benefits of the drug outweigh the risks for many people with RA, especially if other RA medications such as disease-modifying antirheumatic drugs (DMARDs) and nonsteroidal anti-inflammatory drugs (NSAIDs) haven’t worked for them.

Safety and efficacy, however, remain a concern.

The deaths in the AbbVie study weren’t a concern to researchers, however.

One of the deaths was of unknown causes. The second participant died from heart failure and a presumed blood clot that was determined not to have been related to the medication.

According to Reuters, a researcher on the study wrote in a client note, “Following the second positive phase 3 trial… we believe this drug has the potential to be the best-in-class JAK inhibitor. We remain comfortable with its safety profile.”

AbbVie’s spokesperson Jillian Griffin told members of the press, “At the time of initial report, both events were considered by the investigator as having no reasonable possibility of being related to the study drug.”

But AbbVie isn’t the only pharmaceutical company that has caused some concern about the safety of JAK inhibitors

In April, the U.S. Food and Drug Administration (FDA) declined to approve Eli Lilly and Company’s RA drug, baricitinib, also a JAK inhibitor.

FDA officials said the drug needed an additional clinical study due to a small but increased number of potentially dangerous blood clots seen in patients taking baricitinib in clinical trials.

Company officials have said they will file a resubmission by the end of January.

Delays like this can often become more than minor roadblocks and can hold up drug approvals for years.

Currently, Pfizer’s daily pill, Xeljanz, is the only FDA-approved JAK inhibitor drug in the United States that is used to treat RA.

When it was first approved in 2012, some patients were concerned about its safety.

At the time, Europe was holding off on approving it and other JAK inhibitors.

In 2014, patient Heidi Schroeder of Pittsburgh told Healthline, “My doctor won’t put me on it. He said it is too dangerous with my combination of rheumatic and autoimmune conditions.”

But now, Xeljanz remains a commonly prescribed choice for managing moderate to severe cases of RA and has been one of Pfizer’s more successful drugs on the market.

Whether or not there is a future for JAK inhibitors as a common RA treatment remains to be seen.

But with AbbVie and Eli Lilly still pushing forward through clinical trials for Xeljanz rivals, it seems that they will become mainstream staples in managing this disabling condition that affects 1.3 million Americans.