There is no single illness called “depression” or “anxiety” and there are countless variations of each (as I will explain later). For example, whilst many people have depression caused by a lack of serotonin (or impaired serotonergic functioning), many do not. Depression can be caused by faulty thinking, life stressors, low dopamine, low noradrenaline, too much glutamate, thyroid problems and sleep disorders, to name but a few.
