A residual drug or alcohol phenomonon in which, during a period after a heavy binge, only a small amount of the recently-abused substance is needed to re-activate your buzz. So named after what happens in the shower when you "rinse and repeat": only a tiny bit of shampoo is needed the second time around to achieve a full sudsy lather.

When because of recent use, a little goes a long way. Usually referred to when re-gaining an alcohol buzz. (If you shampoo your hair and ever "repeat", you know how just a tiny bit of shampoo will cause instant lather? that's the shampoo effect)

(noun) The effect of having that first drink the next day, after a long night of drinking, and it gives you a good buzz right away. Much like how quickly the shampoo lathers as you apply it the second time.