Everyone wants to be happy, but happiness is nothing more than increased electrical activities in the brain that occur as a reward to motivate us to keep doing the activities that are necessary for survival. People are happy when they get the things they desire, and the things they desire are the things they, directly or indirectly, need to survive.
drugs are not necessary for survival but make people euphoric because they DIRECTLY interfere in the reward mechanism and magnify electrical activities in the brain.