What is it?

Melatonin is an active ingredient in Spark Plus.

From Healthline:

The epigallocatechin gallate (EGCG) in green tea may prevent hair loss by inhibiting the activity of hormones that induce hair loss and promoting hair regrowth by stimulating hair follicles.

Club Roots Products Featuring Melatonin:

Spark Plus, a topical hair regrowth treatment that blocks DHT and stimulates new hair growth in the follicle.