If you monitor your hair line where the fine hair (baby hair) is you can tell very early if hair is growing there or not. Obviously you won’t see the entire hair but you will notice a dark shade were the hair is starting to grow vs a very slick shiny bald area where hair is not growing.As a med student, perhaps I can shed some light. In dermatology, we generally say that it takes at least 6 months to notice thickening/ regrowth. That’s because the hair doesn’t automatically become thicker over time, the follicle has to go through several cycles and becoming progressively thicker with each cycle. This is why when you lose hair, it’s not lost forever immediately, it’ll grow back but thinner everytime until it stops/dies.
However this is a general statement, exceptions always exist. You have people who notice visible regrowth within less than 3 months. So I guess it’s possible to see a reduction of hair loss within a short but seeing regrowth is less likely.
Man I have lost and regain my hair along my hairline so much time lol I had my barber confused lol.