Here a study on Morr-F (0.1% finasteride / 5% minoxidil) including maximum steady-state plasma concentrations:
https://www.omicsonline.org/open-ac...h-androgenetic-alopecia-2155-9554.1000253.pdf
They compare it against finasteride oral (1mg) and state:
The steady state maximum Finasteride concentration was 0.6 ng/mL and exposure Finasteride was found to be 6.3 ng.h/mL. The pharmacokinetic studies with oral Finasteride (1 mg/day) resulted in maximum Finasteride plasma concentration of 9.2 ng/mL and 53 ng.hr/mL. Thus, the Finasteride concentration observed were found about ten-fold lower compared to Finasteride administered orally at similar dose. This was expected as systemic exposure after topical administration is generally lower compared to oral. However, topical administration of Finasteride have indicated no significant statistical differences in the number of terminal hairs, total hair count, and size of alopecia area compared to oral Finasteride after 6 months.
For me the question is really what dose to select based on efficiency vs side-effects. Oral finasteride 0.5mg ED gave me depression that built up slowly over time. I think you hit the saturation point sooner or later. With lower dose it just takes more time. And the plasma concentration of finasteride is not really the problem, it's the steap dose response.
I think I'm going to start with 0.005% finasteride as there is a study that claimed no side-effects over 16! months:
https://www.hairlosstalk.com/interact/threads/topical-finasteride-study-question-for-bryan.42836/
and
https://www.researchgate.net/public...y_evaluations_after_a_16-month_therapy_course