What is depression?
Depression is not just feeling low, which we all feel from time to time. It is a long term feeling of sadness that persists for more than a few weeks and affects your behaviour and quality of life. Depression is an illness, which can range from mild to severe depending on your symptoms. These symptoms include anxiety, loss of interest in your usual activities, disturbed sleep, change in appetite, fatigue, feelings of worthlessness or guilt, difficulty thinking or concentrating, and recurrent thoughts of suicide. This condition is also called Major Depressive Disorder and is one of several mood disorder treated by antidepressants. Other mood disorders include anxiety disorder, bipolar disorder, obsessive-compulsive disorder (OCD), panic disorder and post-traumatic stress disorder (PTSD).
Depression and other mood disorders are thought to be due to an imbalance of brain chemicals called neurotransmitters, particularly serotonin and noradrenaline. These brain chemicals pass messages between nerve cells (neurones) in the area of the brain that regulates mood. When a neurotransmitter is released by one neurone, it passes across the gap between neurones (synapse) and triggers an electrical impulse in the next neurone. Transmission of a nerve signal from one neurone to another allows nerve cells to communicate with each other. Any neurotransmitter remaining in the synapse after release from the first nerve cell (pre-synaptic) and not used by the receiving nerve cell (post-synaptic), is taken up back into the pre-synaptic neurone. This process is called neurotransmitter reuptake.
How do antidepressants work?
Antidepressants are medications that are used to treat symptoms of depression and other mood disorders. They are classed according to how they work and which brain chemicals they target. These include:
- Selective serotonin reuptake inhibitors (SSRI) such as fluoxetine, escitalopram, and sertraline.
- Serotonin noradrenaline reuptake inhibitors (SNRI) such as venlafaxine.
- Tricyclic antidepressants, such as imipramine, and tetracyclic antidepressants such as trazodone, are non-selective neurotransmitter reuptake inhibitors as well as blocking effect of other neurotransmitters like histamine and acetylcholine.