When someone starts out on antidepressants, their neurotransmitter [1] levels return to normal almost immediately. However, patients usually only begin to see improvements 2 - 4 weeks later. This wouldn't be the case if depression was simply due to lowered neurotransmitter levels.

However, all is not lost. A new theory suggests that patients have a lowered rate of neurogenesis (creation of new brain cells) and that serotonin is crucial in kick starting the process.

[1] Patients usually have lowered levels of Serotonin, norepinephrine and dopamine.

To say that depression is a chemical imbalance is to over-simplify the cause and treatment.

People hearing the chemical imbalance hypothesis may think that there's no effective evidence based therapy available, or that they will need meds for the rest of their life, or that they are going to relapse for the rest of their life.

That's not true. There are effective, evidence based, talking therapies. The most well known (Cognitive Behaviour Therapy) is simple to understand, easy to apply, and can be given by therapists or can be self-applied through websites (the Australian "Mood Gym" is one) or books ("mind over matter" is a good example).

A person given just meds will be more likely to relapse than someone given meds and CBT.

> I cannot speak on that and recommend professional help.

Yes, professional help is important. In the UK front line treatment for mild to moderate depression is not medication, but is CBT. And CBT should be used for other illnesses too.

My emphasis on things like CBT is because they have been shown to work; not because I don't think that depression is a "real illness'. See, for example, the use of CBT to treat pain suffered by cancer patients.