Functionality - Upon usage, instantly clears the effects of a drug. However, 50% of the time causes a long >6h "withdrawal" period where you cannot take other drugs. 5% of the time, induces an overdose of that drug (in real life Narcan causes instant intense withdrawal).
Why - Could be useful in situations like wars, if you're on Xanax and quickly need to gear up to fight. Fits the theme of the game. Could allow for more frequent happy jumping