The consumer watchdog group, Public Citizen, this week asked the U.S. Food and Drug Administration not to approve the drug, rivaroxaban (Xarelto), for use in patients with atrial fibrillation, citing concerns over the drug’s overall safety and efficacy.

The group issued a letter to the FDA, specifically addressing a recent discrepancy in opinion between an FDA advisory committee’s recommendation about the drug and a clinical review of the medication. In September, an FDA advisory committee recommended approval of rivaroxaban for stroke prevention in those with atrial fibrillation. However, clinical staff reviewers of the drug said that is should not be approved, citing more tests should be conducted to shed additional light on safety and efficacy issues.

In its letter, Public Citizen wrote, “Given the uncertainty surrounding the efficacy and safety of this drug, and the fact that there are already two existing therapies for the same indication, rivaroxaban should not be approved until appropriate clinical studies are performed.” In addition, the group also outlined concerns surrounding the phase III ROCKET-AF trial for the drug, citing ethical concerns relating to study protocol and conduct.

The FDA is expected to make a final decision regarding the approval of rivaroxaban sometime in November.