Robust outcome data from Randomised Controlled Trials (RCTs) to support the use of specific drugs in specific hypertensive emergencies are lacking.
A recent Cochrane Collaboration Review addressing this issue found that there was no:
There is an acknowledgement that, despite the lack of evidence, it is not hard to accept the necessity of reducing BP in hypertensive emergencies where progressive end organ damage is occurring and, therefore, that placebo controlled trials would be unethical.
It also appears that, with respect to the relative benefits of specific agents, it is a lack of evidence rather than evidence of no benefit due to trials being too small or poorly designed. There is a clear need for further research in this area.