What are antidepressants
The antidepressant drugs in our depression section are used for treatment of depression also know as major depressive disorder, and other mood disorders, such as anxiety disorder, bipolar disorder, obsessive compulsive disorder (OCD) panic disorder and post traumatic stress disorder (PTSD). Although antidepressants have different ways of working, they all influence mood, either as mood enhancers or mood stabilisers, acting directly at the level of the brain to restore the chemical imbalance that is the root cause of depression and anxiety.
Nerve cell communication
All antidepressants interact in some way with specific brain chemicals called neurotransmitters that pass messages between nerve cells (neurones) in the area of the brain that regulates mood. A neurotransmitter released by one neurone passes across the gap between neurones (synapse) and triggers an electrical impulse in the next neurone, setting up a communication signal that is transmitted from one neurone to another and propagation of this signal is how nerve cells communicate.
Serotonin and noradrenaline are important neurotransmitters involved in nerve pathways that regulate mood. They are recycled after use by being taken back into the presynaptic neurone or sending cell after they have initiated transmission of the nerve signal. Once this happens nerve signal transmission stops. If there is insufficient serotonin or noradrenaline released to trigger a nerve signal, then this communication pathway does not work properly and leads to symptoms of depression.
Classes of antidepressant
Each class of antidepressant medication works by a slightly different mechanism to change the amount of mood enhancing neurotransmitters, particularly serotonin and noradrenaline. Most antidepressants boost neurotransmitter levels, improve nerve pathways that control mood and provide prolonged relief from symptoms of depression and other mood disorders. This is achieved by different mechanisms depending on the class of antidepressant drug:
- Selective inhibition of reuptake of neurotransmitters comprise two sub-classes; selective serotonin reuptake inhibitors (SSRI) and serotonin noradrenaline reuptake inhibitors (SNRI). Some reuptake inhibitors are more selective and effective than others but they all keep nerve signals flowing along the mood enhancing pathways.
- Tricyclics are neurotransmitter reuptake inhibitors but they are not selective and affect other neurotransmitters like histamine, with gives them sedative properties; also acetylcholine, which can affect heart rate and blood pressure.
- Reversible inhibitors of monoamine oxidase (RIMA) inhibit the enzyme monoamine oxidase that metabolises and inactivates the neurotransmitters once they have done their job.
- Anxiolytics work by interacting with receptors for the mood enhancing neurotransmitters, particularly serotonin and noradrenaline, prolonging their effect. They also act on dopamine and acetylcholine receptors, which helps reduce symptoms of anxiety.
Other types of antidepressant
There are some drugs that cannot be classified as a group based on the way they work. They are generally non-specific and may work by more than one mechanism including acting directly on neurotransmitter receptors and inhibiting reuptake. One drug in this group has the opposite effect to most antidepressants because it dampens down mood enhancing nerve pathways by reducing the amount of neurotransmitters, which is needed for control of manic depression or bipolar disorder.