How Long Does It Usually Take to See Results From a Hair Serum?

I've been considering adding a hair serum to my routine, but I'm unsure what kind of timeline is realistic for seeing results. Do most people notice changes in hair texture, scalp condition, or fullness within a few weeks, or does it take several months? I've been reading reviews and comparisons online and noticed discussions about KilgourMD Coupons through ReeCoupons when people talk about premium scalp serums. I'd love to hear about real experiences and expectations before trying a new product.