The nominee to head the FDA, the agency that oversees all prescription drugs marketed in the U.S., led a clinical trial that was sharply criticized as biased in favor of the experimental blood thinner Xarelto, according to Project On Government Oversight (POGO).

Robert Califf, President Barack Obama’s FDA nominee, co-chaired the executive committee of the Xarelto clinical trial. A “lack of care” in the trial’s design and execution might have led to avoidable strokes among test subjects, a senior FDA official wrote.

The FDA approved Xarelto in 2011 over the objections of the primary FDA scientists assigned to study its safety and effectiveness. Their review, according to the POGO report, argued that patients could be “at greater risk of harm from stroke and/or bleeding” if they took Xarelto than if they were treated skillfully with warfarin, a blood thinner that has been on the market since the 1950s.

As FDA commissioner, Califf will hold considerable sway over decisions that affect the interests of the drug industry and the health and safety of the public.

“Dr. Califf’s handling of the Xarelto trial raises concerns about his judgment in overseeing the pharmaceutical industry,” said POGO Executive Director Danielle Brian. “As senators consider Dr. Califf’s confirmation to run the FDA, they should ask tough questions about the Xarelto clinical trial.”

Founded in 1981, POGO is a nonpartisan independent watchdog focused on government reforms. POGO investigates corruption, misconduct and conflicts of interest.