Interesting! Is this the article? :
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3521899/
Without in-depth understanding behind it all,this is my take of it:
-Topical caffeine prevents testosterone from negatively affecting growth, but Alpecin shampoo etc are not very effective for the reason that they are simply not absorbed enough into the scalp.
-Any topical shampoos also only act as a weak stimulant (and it barely stays on the scalp for long), so consider it a very weak version of scalp massaging.
-The previous findings had been that drinking caffeine does not cause hair loss. This is from UK's Harley Street Clinic:
"Is caffeine causing my hair loss?
I drink a lot of coffee, is that why I’m losing my hair? This is a question we see a lot. Too much caffeine is not good for you for a lot of different reasons, but hair loss isn’t one of them.
Caffeine is a naturally occurring chemical stimulant. Caffeine is found in beverages we drink on a daily basis such as tea and coffee and is also found in a variety of different fizzy drinks and energy drinks. A number of different studies show the effects of caffeine and hair loss, and they’re positive. Caffeine does not contribute to hair loss or baldness."
I guess the 2018 study disproved that theory with more relevant findings relating to DHT, and drinking coffee/energy drinks should be avoided :/