most likely some of the topical solution is destroyed in the GI tract.
the SULT1A1 sulfates minoxidil at the follicular level, and as the inactive form travels in the bloodstream after sublingual absorption, you minimize hemodynamic effects, allowing dose dependent response for people with low enzymatic activity.
also you have to think about the disadvantages of oral min (IF drinking minoxidil works, and that's a big if), as it is metabolized in the liver, the API (active pharmaceutical ingredient: minoxidil sulfate) is further metabolized by the kidney within 30 minutes, and withdrawn from the bloodstream. sublingual min travels in the bloodstream as its inactive form, allowing higher bioavailability. 90% of oral minoxidil is absorbed in the GI tract, but only 10% is metabolized into its API.
topical solution has an absorption rate of 3-5% when covering the entire scalp, now when applying sublingually, that absorption rate will go up. The oral mucosa is a tissue that allows diffusion of drugs (unlike the skin barrier), and leaving it for 5-10 minutes, you could estimate an absorption of 20%, being conservative.
conclusion, sublingual minoxidil is not only safer, but much more efficacious than drinking topical solution. And ongoing clinical trials for sublingual min will show how it's more efficacious than oral tablets.
you can see the results using .45-.90mg here:
https://www.sinclairdermatology.com...a-retrospective-caseseries-of-64-patients.pdf
and if you watch the video at the start of the thread, you'll understand why sublingual is the way to go
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and we don't have taste buds in the sublingual region, if you let it sit there, it won't taste at all.