Often there is more than one cause of depression. It can be a reaction to something such as bereavement, divorce, redundancy or financial worries. It can also be the consequence of a physical condition such as a poor diet, lack of physical fitness or illnesses, such as flu.
A person is more likely to have a genetic disposition for depression if they inherit the short version of the 5-HTT gene from their parents. However, many people with this gene and a family history of depression do not develop depression. Similarly, people without either this gene or a family history of depression can become depressed.
People with depression have an imbalance of chemicals in the brain. It is not fully known if this imbalance is a result of depression, or the cause of it.
Alcohol and drugs
Drinking excess alcohol and taking drugs, such as cannabis and cocaine, can cause depression.
Depression can also be a side effect of some prescribed medicines.
The thyroid gland controls a person’s metabolic rate. An underactive thyroid can make a person feel depressed. A blood test will reveal if the thyroid’s function is the cause of a person’s depression. If an underactive thyroid is diagnosed, it can be treated successfully with appropriate medication.
An overactive thyroid can have symptoms similar to mania.