A report released by health economists at Brigham and Women’s Hospital in Boston shows that some FDA programs are more successful than others at shortening the time taken to get drugs from early clinical trials to market approval.

Four FDA programs aimed at speeding the path to approval were analyzed, each of which offers its own set of benefits to drug manufacturers. Looking at drug approvals between January 2012 and December 2016, the report found that 105 of the 174 drugs and biologic therapies approved were given the green light under one of the four programs.

The two programs that came out on top were the FDA’s Breakthrough Therapy Designation and the FDA’s Fast Track program.

The Breakthrough Therapy Designation was initiated in 2012 and is awarded to companies developing breakthrough drugs for a given disease. Companies awarded this designation can take advantage of compressed clinical trials, advice and input from dedicated FDA personnel, and a streamlined FDA evaluation process. Over half the drugs awarded Breakthrough Therapy Designation went from initial human clinical trials to FDA approval in 4.8 years or less.

The Fast Track program, which was instituted in 1997, offers similar benefits to the Breakthrough Therapy Designation, but to a lesser extent. This program was designed to encourage the development of, and expedite the review of, drugs to treat serious conditions with unmet medical needs. Drugs that received Fast Track designation went from initial human clinical trials to FDA approval in around 6.1 years on average.

According to the report, the less successful programs were the Accelerated Approval program, and the Priority Review program. The Accelerated Approval Program allows the FDA to use results from clinical trials that measure a therapy’s indirect effects on a disease. The Priority Review program limits the amount of time the FDA can spend reviewing a drug candidate for approval. These programs, both introduced in 1992, did not significantly shorten the approval timeline when compared to the 69 drugs that were approved outside of the four FDA programs. These drugs took an average of around 8 years to go from initial human clinical trials to FDA approval.

According to economists, the results from this report suggest that guidance and advice from FDA evaluators is key when it comes to shortening drug development and approval timelines. This is provided under both the Breakthrough Therapy Designation and the Fast Track program, but not the Accelerated Approval program or the Priority Review program.