There are lots of both prescription and generic drugs that are not approved at all for any reason in the United States.

Some of this I have gathered is do to funding and historical reasons they were not approved and not necessarily because they are unsafe.

Can Doctors in the United States prescribe these drugs because they are in a grey area or are they off limits?

An example drug that I might be referring to is Solian. Australia has it approved and parts of Europe yet not the US or Canada.