Here's the advice the last FDA commissioner has for his successor

President Donald Trump has repeatedly criticized the Food and Drug Administration for approving drugs too slowly. Yet the pharmaceutical industry has largely applauded the direction of the regulator in recent years.

Rigorous clinical trials are necessary, former FDA commissioner Dr. Robert Califf told CNBC in an interview at the World Medical Innovation Forum in Boston. And while he said patient advocacy is powerful — and that heart disease is an area that could benefit from increased patient demand for reimbursement of new therapies — Califf argued advocacy doesn't change the FDA's decisions.

He also had a few words of advice for his Trump-nominated successor, Dr. Scott Gottlieb. Gottlieb received a positive vote from a Senate committee last week, and now awaits confirmation from the full Senate.