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West London NHS Trust > Patients and carers > Mental and physical health conditions > Depression > Causes of depression

Causes of depression

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.

Family history

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.

Chemical imbalance

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.

Prescribed medicines

Depression can also be a side effect of some prescribed medicines.

Underactive thyroid

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.