Welcome Sarin and thanks for bringing this thread out into the open again as I hadn't seen it before.
I've just spent maybe half an hour reading through this thread from the beginning and feeling constant moments of recognition of my own experiences. Also I note how many of the people who posted on this thread are no longer posting on the forum - and I wonder if they are ok ...
I have experienced many periods of low mood and energy throughout my life and I have also worked in mental health services - and I'm in my 50s - so I have had a long time to think about the issue of depression.
In my experience the type of clinical depression which Monster described where it comes from nowhere and is very severe, is extremely rare. In those cases medications can be very useful but also exercise and slow engagement back into meaningful activities - in a graded way to build up tolerance - can be very useful. I don't think it's true though to say that all other forms of low mood aren't really depression because persistent low mood through dissatisfaction is a form of depression too. But I also agree that the term is way overused nowadays as there is a bit of a 'cult of happiness' thing going on where everyone is supposed to be happy all the time or there's something wrong with you and it needs 'fixing'. Personally I think that is simply a way to market happy pills like Prozac and keep therapists and counsellors in work.
So in response to the OP - are INTPs more prone to depression, here's my tuppence worth.
The question of whether depression is caused by chemical imbalance is unclear. It could be in some cases- it's certainly true that depression occurs if there is an underactive thyroid function, for example, but does that necessarily mean it is always caused by a chemical imbalance, in the sense that the first stage is something creates a chemical imbalance and then the person gets depressed? That is unprovable. If you looked at the brain of a depressed person it is possible that you would see a change in brain chemicals, but if you induced a fit of laughing you would also see a change in chemical balance. So it's impossible to say if depression is caused by chemical imbalance or is manifested by a particular chemical signature. It's not a useful starting point and I think is probably best discounted.
Nonetheless there are some really important things that we know about people who get depressed:
It's more prevalent in people who feel powerless but have responsibilities (if you are powerless but no responsibility or responsibility and power you are not likely to get depressed)
It's more prevalent in people who have an internal locus of control - yes, you believe that you are responsible for making your own world, but if things go wrong you will blame yourself. Those whingers who think the world owes them a living also blame everyone else when things go wrong and that is protective!!!
It's more prevalent in people who are not doing a job/role which matches their level of ability or corresponds to their interests or values - I think that one is self-explanatory
It's more prevalent in people who do not have a strong supportive social network - that doesn't mean you have lots of friends, it means you have people who you feel understand you and have your interests at heart and behave accordingly.
It's more prevalent in people who mess around with their patterns of sleep, food and exercise
OK - so does being INTP make you more likely to end up in the position of fulfilling one of those risk factors? I think so - I think if you look back through the posts in this thread you will find evidence of at least one of these factors being cited by each person who's posted.
I think Sarin's right that it's expressed differently by ES types than ITs and that's partly why I wrote the two threads - one on emotional intelligence and the other on types of therapy best suited to INTPs - you can find them by clicking on my avatar, opening my public profile and looking for threads I've started. I think INTPs more than any type are the *least* helped by psychiatry, psychotherapy and counselling but unfortunately most often referred, especially as teenagers in the US if this forum is anything to go by. This is because the predominant 'wisdom' is that talking about your problems helps - NOT for an INTP! It mostly makes things worse through confusing, compounding and scaring the INTP, making them feel more and more inadequate and fucked up for no being able to engage in the process especially as the counsellors are usually 'nice' people who just want to help - so the INTP is made to feel bad for apparently 'resisting' help or 'rejecting' it.
OK so what helps?
1.
Finding a point of power. You might not be able to control other people, your teachers, your parents, your partner, your boss, your friends, but there are some things you can control - maybe how much time you spend with them, what you choose to share, things you can do which they can't control like blogging, writing, forums etc. Making plans for changing your life towards a point where you have more control - being educated, financially independent, living somewhere else and so on - this will vary from person to person of course!
2.
Develop your ability to discern which things are to do with you and which are to do with other people. Take responsibility when appropriate but don't be afraid to put the blame out there when appropriate. The corny old
Serenity Prayer is actually quite good for this! You don't need to believe in God to get the wisdom of it.
3. Try and do a job or role which is just the right challenge and fits with your interests and values - this is easier said than done especially for INTPs but it is really worth trying. It might involve knuckling down and getting that good education even though you think school sucks because ultimately it'll reduce the risk of ending up in a dead end job working for idiots - I say 'reduce the risk' because most managers are idiots. But this is something really worth putting effort into because it is your ticket to some kind of possibility which you won't have if you have no qualifications. It's easier to drop out and live on an island if you studied physics, engineering and biology!! Really take the time to work out what matters to you - then you are less likely to make a stupid career choice you'll regret. Get independent confirmation of your intelligence, ability and skills - lots of INTPs believe idiot teachers even though they rebel against them. I am speaking from experience here
4. Be very selective about who you have as a friend Didyouknow - I promise things will get a lot better when the rest of the world grows up!! This is a huge problem for teen INTPs because they have to endure teenagers who are fickle, bitchy, arrogant and prattish all around them while they are desperately trying to find someone to discuss the blossoming thoughts and cognitive structures which are forming in their brains. My daughter cries that her girlfriends can't discuss physics with her. But finding supportive friends is very important - you will know them when you find them and hold on tight to them - make the effort to keep in touch and remember their birthdays! (Although many good friends to INTPs forgive us easily for such transgressions) Find allies at work. INTJs trust no one, we tend to be a bit naive I think.
5. Hard though it may be try to establish good sleep patterns, eat sensibly and exercise regularly. If you are feeling low then go for a brisk walk. I know you don't want to, but there is so much evidence that exercise improves mood, use your reasonable side to force yourself up and out!!
There are some other things that I think are helpful to INTPs:
Meditation - simple sitting meditation where you allow your thoughts to arise and fade away and your emotions arise and fade away without engaging with them. It's a simple process but hard. Basically just focus on breathing in and out normally, without forcing yourself to and when you notice that you've gone off on a thought or feeling, just stop and go back to noticing your breath. If you practice this regularly, you will gain control over your thoughts, being able to bat away negative thoughts which bring down your mood, and also ride the bad feelings of misery or loneliness because you know they are transient. There is
an interesting article here about the effects of mindfulness meditation
Develop your emotional intelligence - nothing dramatic - you don't have to become a 'feeler'!!, just try and notice what you are feeling (rather than intuiting or thinking or perceiving) because you might be able to nip problematic situations in the bud and protect yourself from going into a more severe or distressing reaction.
An ex-boyfriend of mine once said he thought I had had 'underlying depression' all my life. Then he went and dumped me and I found out he'd been having affairs behind my back. No I don't have underlying depression - I actually feel like shit when people treat me like that and I have every right to! Seriously though, I'm sure that we INTPs are currently living in an age where being remotely serious, saddened by things and finding it hard to be appreciated is even more difficult. We are all supposed to be consumers now to satisfy the capitalist dream and intellectuals are not very popular. Even universities are no longer the bastion of liberal education, just the manufacturer of the workforce. Dark times.
and on that depressing note my final bit of advice ... don't worry about being unhappy, just don't give in to despair.