DHT Fighting shampoo? There is no such thing, or I highly doubt it works.
Shampoo washes out, so I don't think it will have a lasting affect.
Those shampoos are a complete waste of money. Total bullshit.
I'm assuming that this is what he purchased: https://hairlossdhtshampoo.com/products/dht-blocking-hair-loss-shampoo-conditioner-set
39$ down the drain