Experts believe genetic traits, along with stressful events, illness, medications, or other factors, can lead to an imbalance of certain brain chemicals called neurotransmitters, causing depression. Conditions that may trigger depression include:

• Some medications, such as steroids or narcotics for pain relief. After the medication is stopped, the depressive symptoms usually disappear.
• Problems with hormones, such as imbalances in the thyroid or adrenal glands.
• Chemical imbalances, such as imbalances in blood calcium levels or low iron levels (anemia).
• Long-term (chronic) diseases, such as arthritis, heart disease, or cancer.
• Infections, such as viral infections or infections in the liver or brain.
• Social stressors, such as the death of a loved one.
• Chronic stressors, such as living in poverty, having family difficulties, or having serious medical problems or living with someone who does. Older adults who move from an independent lifestyle to one that is more dependent upon others often experience depression.
• Social and peer pressures in children and teens. For more information, see the topic Depression in Children and Teens.
• Drinking alcohol, using illegal drugs, or having a substance abuse problem.
• Other conditions, such as menopause or chronic pain, stress, or fatigue.
• Recent childbirth. For more information, see the topic Postpartum Depression.