[F]ewer than 2% of all drugs that are investigated by academics in preclinical trials are ultimately approved for sale. A recent study found that just 1 in 5 drugs that were successful after Stage 1 trials made it through the FDA approval process.
Even after drugs are approved for sale at the completion of the complex FDA process (involving multiple RCTs), new evidence often emerges casting those initial results in doubt. There’s a 1 in 3 chance that an approved drug is assigned a black-box warning or similar caution post-approval. And in most cases, the effectiveness of a drug in real-world settings, where it is prescribed by harried physicians and taken by distracted patients, is much lower than its effectiveness in trial settings, where the investigative team is singularly focused on ensuring that the trial adheres to the sponsor’s conditions —or where an academic investigator is focused on publishing a first-class paper.
Source: Sherry Glied quoted by Timothy Taylor
Also, both authors are very good on why RCTs (randomized controlled trials) rarely produce workable reforms for reducing crime or improving educational results.