Referring this question to Dr. Hatem Al-Haj , Profession Dean of Shari`ah Academy of America , he said;

First of all, as far as accountability, if one has insight and can still sort out right from wrong, s/he should not assume that the religious obligations do not pertain to them. Once someone is entertaining the question, it means they have enough insight to be accountable. As for the severe depression that could become incapacitating, one should do his/her best and Allah is the best judge.

Secondly, as for being depressed, here is my advice for prevention and treatment in bullets:

(1) At-Tawheed

It is only expected that one who serves more than one deity will be distressed. Allah says:

“Allah puts forth a Parable a man belonging to many partners at variance with each other, and a man belonging entirely to one master: are those two equal in comparison? Praise be to Allah. But most of them have no knowledge.” (Az-Zumar, 39:29)

If there is only one your heart is attached to and you try to please, you will feel that the task of your life is doable and clear.

(2) Belief in destiny

Allah is the one in control. No Dualism in Islam, Allah said, “Allah is the Creator of all things, and He is the Guardian and Disposer of all affairs.” ( Az-Zumar, 39:62) and Allah is the controller of all things: “No calamity befalls on the Earth or in yourselves but is inscribed in the book of decrees before we bring it into existence verily that is easy for Allah. In order that you may not be sad over matters that you fall to get or rejoice excessively because of that which has been given to you and Allah likes not prideful Boosters”

Put your trust in Him and serve Him and know that you can’t change His decrees. You can only do your best to avoid harm. The one who tested you is the only one who can relieve you.

(3) Certainty in the great reward stored for the patient. Allah said,

“And certainly we shall test you with something of fear, hunger, loss of wealth, lives and fruits. But give Glad tidings to the patient who when afflicted with calamity say truly to Allah we belong & truly to him we shall return. They are those on whom are Salawat (blessings & forgiveness) from their lord & mercy, and it is they who are the guided ones”

(4) Knowing the true value and worth of this life.

Allah said,

“Know that the life of this world is only play and amusement. Pomp and mutual boasting among you and rivalry in respect of wealth and children, as the likeness of vegetation after rain there of the growth is pleasing to the tiller afterwards it dries up and you see it turning yellow then it becomes straw. But in the hereafter there is a seven torment and there is forgiveness from Allah and good pleasure, whereas the life of the world is only a deceiving enjoyment.”

Is this transient life of deceiving enjoyment worth much grief over it?

(5) Having higher aspirations and goals…we do not get consumed in our own problems.

(6) Mixing with the right crowd

A WISE FRIEND IS A TREASURE, and to rely on Allah alone doesn’t mean that you may not vent out to a wise righteous friend who may entertain you, or give you good advice, or help you in other ways.

(7) Learn to be a minimalist or close

Abu ad-Darda’ (may Allah be pleased with him) would say:

“O Allah, I seek refuge in you from the diversion of the heart” and when he was asked about this, he would say: “To have riches and possessions in every valley. He who is in need of the donya has no donya [no happiness in the donya]”

That doesn’t mean Allah forbade the enjoyments of this dunya, but the aggressive pursuit of them could lead to the grief.

(8) Recreation

Smiling livens the heart; Abdullah ibn al Harith tells us about the prophet (peace be upon him) saying that he had never seen someone smile at the other’s face as the prophet Muhammad (peace be upon him) used to do.

(9) SUPPLICATIONS

Allah says:

“Or, who listens to the distressed (soul) when he calls on Him, and who relieves his suffering?”. (An -Naml 27:62)

The following supplications are particularly useful in times of hardship,

“Verily distress has seized me and You are the most merciful of all those who show mercy!” (Al Anbiyaa’ 21:83)

(10) Medicine and Life style changes

Medicine may be needed, but try also healthy life style.

Exercise…lose weight…natural foods with fiber and less meat…expose yourself to the sun…learn to relax…

The Messenger of Allah said with regard to medicine for mental health: “Verily, at-Talbeenah [boiled barley with honey] brings well being to the heart and takes away some of one’s sadness.”

Barley has tryptophan, which is a precursor of serotonin, and important neurotransmitter in the brain that causes mood elevation.