A mental illness is caused by damage on certain parts of brain, resulting in disturbed functioning of the brain cells, such as abnormal transmission of the chemical among brain cells. Such disturbance inside the brain manifests as mental symptoms involving cognitive function, content of thought, perception, emotion, behaviour and biological function (e.g. sleep and appetite) and impaired overall functioning of the person.
Generally, psychiatric medications work by restoring balance of chemicals in brain. For example, an antipsychotic normalizes the transmission of a chemical known as dopamine, and therefore, makes delusion subside. Some medication might even promote the healing of brain. For example, an antidepressant works by restoring the normal transmission of a chemical called serotonin among the brain cells, as well as promoting the healing of damaged part of brain through a growth factor called brain-derived neurotrophic factor (BNDF).
Common types of psychiatric medications include antidepressants, antipsychotics, mood stabilizers, tranquilizers and hypnotics, and anti-dementia agents etc. However, this traditional way of classifying psychiatric medications is actually imprecise. For example, the medications used to treat depression are also useful in treating anxiety disorders. Mood stabilizers, including lithium and anticonvulsants, are the main-stream medications for bipolar affective disorders; however, the new generation antipsychotics are found to have therapeutic effect on bipolar affective disorder as well.
Antidepressants are medications which are used to treat depressive disorders. Currently, the common types of antidepressant include Tricyclics, Selective Serotonin Reuptake Inhibitors (SSRI) and Serotonin and Noradrenaline Reuptake Inhibitors (SNRI).
The disease mechanism of depression is that there are damages on the parts of the brain which regulate mood, motivation, memory, sleep and appetite etc. One channel to such damages is a chronic exposure to abnormally high level of stress hormone which is toxic to the brain. In these parts of the brain, a number of chemicals, such as serotonin and norepinephrine, are important for functioning. The transmission of serotonin is disrupted in the diseased part of the brain, leading to malfunction of the brain.
An antidepressant works by at least two ways. On one hand, it directly enhances the transmission of serotonin among the brain cells. On the other hand, it promotes the healing of damaged parts of the brain through a growth factor called brain-derived neurotrophic factor (BNDF). Stress hormone damages the brain by inhibiting the production of this brain growth factor, causing the brain cells to wither like the root of a plant drying up.
Delusion is one of the key symptoms of psychosis. To understand how antipsychotic can relieve a delusion, we have to know what abnormality in brain causes the formation of delusion.
In the brain, dopamine is one important chemical which allows our brain to give us the sense of “personal significance” and “drive” to something in the environment. To survive in an environment, the nerves in our brain release dopamine as appropriately as possible, so that we can reason something to have a personal meaning only when there is some objective evidence. This belief is driven by what really happened in the environment. However, when dopamine is excessively and inappropriately released in the brain, the inappropriately released dopamine made a person have a wrong sense of personal significance towards things in the environment.
Most antipsychotics work by inhibiting the excessive dopamine activities in the brain so that no more “abnormal personal significance” can be attached to things around the person (i.e. no more new delusion developed).
Tranquilizers and hypnotics work by enhancing the activities of a chemical in brain called GABA . The action of GABA is inhibitory. Therefore, GABA action can lower the level of arousal of a person, relieve anxiety and promote sleep.
However, tranquilizers and hypnotics cannot correct the underlying chemical imbalance which causes the abnormal level of anxiety and difficulty in sleep. Moreover, there is a risk of dependence after prolonged use of tranquilizers and hypnotics.
The major medication treatment for anxiety disorder is SSRI and SNRI which correct the imbalance of neurotransmitters. Tranquilizers and hypnotics are limited to short-term use in anxiety disorder and depression. It is easily overlooked that sleep problem is common in anxiety disorder and depression. After anxiety disorder and depression have been treated, the sleep problem will then improve.
