i didnt read the other replies because im a lazy bastard, and also becasue otehr peoples opinions affect your own without youknowing it
anyway yes, it is possible.
your brain is basically a machine, with shitloads of small moving parts, with interconnecting and overlapping functions/chemical flows/patterns etc. memories trigger these flows. experiences trigger these flows. thought processes trigger these flows. visual images/sounds trigger these flows. depending on what chemicals are released when, and where, and what other chemicals were already there in the first place, and how all your cells were handling it at the time, you end up with an EMOTION.
its complicated as shit, but the important principle for everyone to understand is that it is a machine, and can be fixed like one. you fix it by getting more chemical flows that result in positive emotions, while cutting back on the ones that result in negative emotions.
the other important principle is that it all works in a cascade - one emotion causes another ot be felt, which causes another to be felt, and on and on and on in a predictable way and so in this way you can experience extreme emotional states ie even though you might have a few pretty good things happen in your life which cause 'happy' emotions, the negative ones youve been having for the past 6 months beget more negative emotions, and so offset the happy ones. then a few truly bad things happen to you, and you sink and sink and sink into a spiral of ever increasing negative emotions
drugs are useful in that you can biochemically cause the release of a bunch of 'happy' chemicals, and so tip the balance towards happiness in that way. other drugs dull you to the influence of unhappy emotions. the good thing about drugs is taht theyre predictable - you take 100mg of this drug, and youll get xyz amount of that chemical released, and its pushing you in the 'happy' direction, so that you can fix up your life to make more truly positive events occur, which themselves cause the release of happy chemicals and so you stay happy.
you CAN make this happen without drugs, but it takes a lot more effort, because you ahve to do as many positive things as you can while downplaying as many negative things as you can ie stay away from other negative people, hang out with positive people, learn to distract yoursefl away from negative thoughts, learn to play up positive thoughts etc. all of this is very doable, but takes a concentrated effort and energy that is sometimes difficult to come up with when yorue feeling like crap.
anyway its a bit of a wordy reply but its a good way to look at things. play up the good stuff, play down the bad stuff, try your best to alter your behaviour to make this a way of life, until those positive emotional flows gain critical mass and start to feed off each other, and you start feeling better and better, until you buoy out and qualify as being 'normal'
so yah. there you go.