Here is how it works in a nutshell.

Corporations, especially drug companies will sell anything for a buck.
Thanks to regulations drug companies have to submit their product and test trial findings. The only time NIH will do human or other animal trials is when private companies formally refuse to do so. An example of a trial only the government can do is an Ebola vaccine.

There are times when a drug undergoes government testing and trials when a prior agreement exists guaranteeing the Government shares a percentage of future sales.

When the NIH develops a medicine it is made available via a licensing agreement.

Drug companies try to get government grant money but there are loyal government employees who separate the wheat from the chaff and the fraudulent via research and economic scrutiny.

The FDA has no unfailing respect for the NIH and visa versa.
The CDC however has the rapt attention of the NIH and the FDA.

And I view certain Pharmaceutical giants as greedy motherfuckers that do things that Goldman Sachs employees only wish they could do.