Based on your answers, your follicles are likely being miniaturised by DHT while losing their oestrogen protection. That is a root cause, and it is one of the few that is actually addressable.
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The Full Routine, Nothing Left Out
The internal formula in both formats, the Regrowth Complex Serum for your scalp, and the Root Activating Derma Roller included free. The roller preps the scalp before you apply the serum, so more of it reaches the follicle instead of sitting on the surface.
DHT Protection Bundle
You already tried biotin and thickening shampoos. Here is the gap they left: biotin feeds the hair shaft but cannot stop the hormone shrinking the follicle. Shampoos work at the surface. The root issue is internal hormone signalling. Neither addressed DHT.