no one on this forum knows how much you need to put on your scalp each day, or what liquid will give you the best absorption without irritating your scalp.
here are some numbers, though.
0.2mg finasteride grows 80% as much hair as 1mg, which grows 80% as much as 5mg.
the dht produced in the hair follicle for the hair follicle is by far the biggest cause of hair loss. the contribution from dht in the blood is so small that when researchers transplanted a balding hair out of the scalp onto an arm, it went bald just as fast as the hairs it used to be next to. also when they used a drug that stopped dht production in just the sebum glands, it had no measureable effect on hair loss. side effects come from systemic absorption, and hair loss treatment comes from stopping the dht production in just the follicle. some topical finasteride experiments did treat facial hair on women, showing that it can be absorbed. but the right liquid to use is in question. i think minoxidil is your best bet. skin absorption occurs primarily though the pours, and sweating during applicaiton can push it back out some.
We don't know how long finasteride would linger in your scalp before getting washed away in the blood, but we know from graphs that once it is in the blood, it enters cells fast and shuts down 2/3 of the dht that will be shut down in just 1-2 hours. I've seen on graphs that cells absorb 2/3 of the finasteride theywill absorb that day in the first 1-2 hours. so if it is absorbing through your scalp over 2 hours, you are probably safe for the whole day, since dht levels take 3-4 days to rise 50%.
1.5-5% of minoxidil is absorbed through the scalp. so if 1mL of 5% minoxidil has 50mg of minoxidil, only 2.5 mg is absorbed, and the rest dries to a yellow powder that looks like dandruff.
the finasteride molecule is very similar looking to testosterone, which is how it competes for the 5ar2 enzyme.
30% of the testosterone in testosterone patches is absorbed through the skin in 23 hours. They are 12g patches, and about 4 goes in.
60% of finasteride is absorbed in your gut, so if you take a 5mg pill, only 3mg enters your blood.
If you weigh 80kg, and your scalp is 1cm deep, then the 200cm2 male pattern baldness area is 1/400th the volume of your body, which means a little goes a long way.
If you want your scalp to get the same benifit that 1mg/day orally would give, and if 5% were absorbed though your scalp, you would need 1mg / 400 * 0.6 / 0.05 in that order, which equals 0.03 mg per day, and your body would get 0.03mg * 0.05= 0.0015 mg per day of used finasteride. however, you might only absorb 1%, and maybe 2/3 will rinse away in the blood before getting to your follicles. this would mean you would need 0.03*5*3= 0.45 mg per day, which is 1 pill every 10 days. In case you don't grind the pill well enough, and some of it's unexposed volume has finasteride that is not dissolved, you might want to error on using 1 pill per week. If the 1% estimate is wrong, and actually 5% is aborbed, then your body will get 0.45/5= 0.09 mg per day. this is still less than 1/5 what you are taking now.
So try 1 pill per week, and if you get sides, you know you are getting enough and can reduce the dose, and if you don't get sides, you can raise the dose and see when you do and then cut back. And please tell us all what that dose is, since those of us without side effects can't do this experiment like you can.
people who get side effects from finasteride are an asset to the rest of us because they can tell us what dose is necessary to get enough finasteride in our bodies so we don't have to pay for dht tests.
