Imbalance of brain chemicals called neurotransmitters - Changes in these brain chemicals may cause or contribute to clinical depression. Certain diseases or illnesses - Ailments such as cancer, heart disease, Parkinson's disease, Alzheimer's disease, diabetes and hormonal disorders can often trigger clinical depression. This is referred to as co-occurring depression. A genetic history of clinical depression can increase one's risk for developing the illness. But depression also occurs in people who have had no family members with depression.
Some medication can actually cause clinical depression.
Therefore, it is important that people inform their doctors of all medications they are taking and report any depressive symptoms. Drinking large amounts of alcohol on a regular basis can sometimes lead to clinical depression. Excessive alcohol consumption is also sometimes a symptom of depression.