In fact, if you wash your hair several times a day, an additional application of the Plantur 21 Nutri-Caffeine Elixir​​​​​​​ is actually recommended. It is impossible to overdose because the quantity of caffeine that is absorbed by the hair follicle and scalp is roughly equivalent to about half a cup of coffee. The quantity is entirely harmless, even for people who react sensitively to caffeine. In addition, the active ingredient is applied locally to the scalp; the quantities that disseminate throughout the organism from there are negligible.