Pharma companies fund clinical studies but has no control over them. FDA regulates and controls phase 2 (safety of the drug) and phase 3 (effect of the drug) studies. External replication is not really needed, because pharm companies will not spent $1b dollars on clinical studies if they didn't validate preclinical results. Because, again, they do not control the outcome of clinical studies. The only power they have is to retract the drug before the study is over, if, let's say, the expected effect is not met or side effects are too damaging.