Maybe topical + oral is very good. But no research on it.
The issue is that it is not known how well does the topical prevent hair loss compared to the oral, there is simply no research quite like the original 1mg pill has.
Of course that there is not, cause Merck patent it as oral . But, there are studies, pubmed it , and what do you think will be faster reach the follicle? since is have a low molecular weight ? Apply direct to the scalp or take it orally, by pass the stomach, the liver , going to all the organs, etc ? Again, is brainless use it orally . Specially cause it have a molecular weight of only 372.549 g/mol . Much more finasteride will reach the active site than if you take it orally, the prove are the studies where it show that orally finasteride supress 70 % of systemic DHT but only around 40 % on the scalp. If you want to reach the follicles, and if you don't need liver convertion and if the molecular weight allow it, the smarter thing to reach the follicle is applying topically .
For example, most topical studies that compare it with oral, are 1 % finasteride . 1 %, if you apply 2ml daily , will be applying 20mg of finasteride to the scalp. See how a none sense it is ? Cause, even if a low dose go systemic, you will have 2mg of finasteride systemic and ofcourse that will eliminate as much as DHT than oral and will cause same side effects ! Now, who pay for this studies ? Merck. Cause they are telling, " keep it use it orally, it is the same and it is easier "
Why they don't do that kind of studies with 0.1 % or 0.01% ? That will be the smarter thing to do . Same results than orally , same local inhibition, but much lower systemic inhibition, aka, less side effects .