finasteride is not soluble in water. mix 5-10% octyl salicylate into water/ethanol/propylene glycol for your topical finasteride, though extract the finasteride with just the ethanol before mixing it up, so the filler settles faster. Yes, it is effective. 20% water, 50% ethanol, 20% PG, 10% octyl salicylate is the best I've heard of, though I'd add some DMSO too, like 3%. I believe in using a mixture of penetration enhancers.
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Guy with the GTE:
the GTE will probably not block all the androgen activity. Add Apple poly to the mix to stop some of what happens after DHT bonds to the receptor. Your mix sounds good, though I prefer to add other penetration enhancers. For a water soluble med, octyl salicylate won't work, or at least won't be that soluble. I'd add some ethanol in there, though not a lot. for a total of 5 oz (300g of liquid) I'd use 15g of powder tops. I suspect the powder is 2g per mL. I think there are 5mL in a tea spoon. So I'd do one 1 tea spoon (flat) of GTE and 2-3 500mg apple poly capsules in the 5 oz. Just what I'd do. Please let us know how it feels or if it cakes much.
The problem with being right at the saturation point is that when you put it on your head and it first starts to evaporate, some will precipitate out of solution into the solid form, which does not enter pores and may block then. I think you should be at 1/2 the saturation point instead.