What is a good shampoo for hair loss?

My son's scalp is getting thinner and thinner...

My son, who is studying, seems to be under a lot of stress; his hair is thinning, and I especially feel like the crown of his head is getting wider.

I've been buying shampoos that are supposed to be pretty good, but

I've been using tea tree shampoo recently because I heard it was good, but

Are there any good products for male hair loss?