Merck Manual

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Quick Facts



The Manual's Editorial Staff

Last full review/revision Oct 2019| Content last modified Oct 2019
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What is depression?

Depression is feeling too sad or sluggish to do your daily tasks or take part in activities you usually enjoy.

What causes depression?

Doctors don’t know exactly what causes depression. You may be more likely to get depression if you:

  • Have family members who have or have had depression

  • Are a woman—hormone levels can cause mood changes, especially before a menstrual period or after having a baby

  • Go through an emotional event, such as a natural disaster (such as a hurricane), serious illness, or death of a family member

  • Have serious health problems, such as cancer

  • Take medicines that have depression as a possible side effect

Depression is more common when there is less daylight, such as in fall and winter.

What are the symptoms of depression?

Symptoms can start little by little.

  • Losing interest in activities that you used to enjoy

  • Feeling worthless, guilty, or lonely

  • Feeling hopeless

  • Changes in sleep habits, such as sleeping more, having trouble falling asleep, or waking up early in the morning

  • Weight loss or gain

  • Trouble concentrating and making decisions

  • Drinking alcohol, smoking, or using drugs more than usual

  • Thinking about death and suicide

How can doctors tell if I have depression?

Doctors will suspect depression based on your symptoms and a family history of depression. They’ll also ask questions to see how severe your depression is. To find out if a health problem is causing your depression, doctors may do tests, such as blood tests.

How do doctors treat depression?

Doctors may:

  • Prescribe antidepressant medicine

  • Provide individual or group counseling (psychotherapy)

  • Tell you to take walks and visit with friends and family

  • Invite you to a support group to share your feelings with other people

  • Admit you to the hospital if you’re thinking of suicide or if you attempt it

If you have severe depression, doctors may do electroconvulsive therapy (once called shock therapy). In electroconvulsive therapy, your doctor will put you to sleep with medicines and then send an electric current through your brain. Doctors don't know why, but the electric current often helps depression go away.

If your depression usually happens in the fall and winter, doctors may have you look into bright lights that mimic sunlight (phototherapy).

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Preventive Health Care Visits in Infants
Frequent doctor visits are recommended for all infants younger than 1 year of age. These visits, also called well-child visits, make it possible to check development, look for health problems, provide age-appropriate vaccinations, and educate parents. Which of the following is a condition that might affect some infants born very prematurely, with less than 32 weeks of development in the uterus?
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