I think I looked into it when I started with finasteride, on 1mg now, but thinking about reducing. I'll post a bit of what I found then for you: from
https://www.hairlosstalk.com/intera...ical-and-oral-finasteride.123959/post-1829207
"RESULTS:
Scalp skin DHT levels declined significantly by 13.0% with placebo and by 14.9%, 61.6%, 56. 5%, 64.1%, and 69.4% with 0.01, 0.05, 0.2, 1, and 5 mg doses of finasteride, respectively. Serum DHT levels declined significantly (P <.001) by 49.5%, 68.6%, 71.4%, and 72.2% in the 0.05, 0.2, 1, and 5 mg finasteride treatment groups, respectively." (3)
Meaning that 0.5mg finasteride is very close to one and five mg finasteride. Never in the paper is it discussed that a higher dose should be used because of the half-life etc. Therefore their conclusion was: "Doses of finasteride as low as 0.2 mg per day maximally decreased both scalp skin and serum DHT levels. These data support the rationale used to conduct clinical trials in men with male pattern hair loss at doses of finasteride between 0.2 and 5 mg."
The 1mg could as well have been 0.2 or 0.5 or 2mg for that matter, as long as it was higher than 0.2. Therefore, there is good rational to deviate from the 1mg and use 0.5mg if you want to, for instance, safe money or (speculatively) lower adverse effects.
There are little studies that studied a dosage of less than 1mg of finasteride. But I don't see a reason why 0.5mg finasteride each day is that much worse than 1mg finasteride each day.
1)
https://www.ncbi.nlm.nih.gov/books/NBK513329/
2)
http://martinelangsam.com/wp-conten...l-Medicine-Article-published-in-Forum-USA.pdf
3)
https://www.ncbi.nlm.nih.gov/pubmed/10495374
