This was in the news in 2018 when the Advertising Standards Authority (ASA) ruled that makers of Alpecin caffeine shampoo could no longer advertise that their shampoo could reduce hair loss. The reason they gave was that there was not adequate evidence to support their claim.
The ASA stated, “Taking into account the body of evidence as a whole, we considered that we had not seen any studies of the actual product as used by consumers on their scalp using an accurate and objective analysis of hair growth, in a well-designed and well-conducted trial.
“We concluded that the claim ‘it can actually help to reduce hair loss’ had not been substantiated and was therefore misleading.”
Any product that advertises a medicinal health claim, must show robust clinical evidence to prove it.