The relationship between obsessive-compulsive disorder (OCD) and depression is deep and complex.

Understanding why these two conditions often co-occur — and perhaps more important, how to think about treatment when you have both — may help you develop better mental and physical health.

Here are some good things to know.

People often have OCD and depression at the same time. The International OCD Foundation estimates that between 25 and 50 percent of those with OCD will also experience depression. Most people experience the symptoms of OCD first, but for a small percentage, the two conditions begin at the same time. It’s rare for depression symptoms to precede OCD.

For that reason, researchers often say that depression is part of OCD, but OCD is not necessarily part of depression.

Does depression cause OCD?

Although it isn’t clear exactly what causes OCD, no research suggests that depression causes OCD. According to the National Institute of Mental Health, OCD may be caused by:

Does OCD cause depression?

The short answer is that yes, it may. Because depression often begins after OCD symptoms develop, researchers think the difficulties of living with OCD can lead to depression symptoms.

Depression may develop because of:

  • the nature of your compulsive thoughts
  • difficulties caused by compulsive actions
  • the problems OCD causes in your life and relationships

Obsessions and depression

OCD may spark repetitive, unwanted, and upsetting thoughts. For many people, the very nature of the thoughts is enough to cause shock, fear, and eventually depression. Here’s an example of how that progression can work.

A new parent might have sudden, unwanted thoughts of harming the baby. About half of all parents (fathers and mothers) have intrusive thoughts exactly like these.

The thoughts can be frightening and cause enormous shame, even though the baby may never be in any actual danger. A parent who doesn’t realize how common these thoughts are might feel that something is wrong with them.

OCD causes intrusive thoughts like these and others. Not all intrusive thoughts involve violent imagery, but most are disturbing or unsettling.

Still, intrusive thoughts do not automatically indicate an increased risk of harm. But that risk may increase if the thoughts occur along with anxiety, depression, and OCD.

Compulsions and depression

In response to intrusive thoughts, people with OCD usually perform specific actions in the mistaken belief that their behaviors will either make the thoughts go away or prevent something bad from happening.

These compulsive behaviors must be performed flawlessly every time — a standard that is hard to meet.

Researchers say this kind of relentless perfectionism, the hallmark of OCD, is also a key factor in depression.

Functioning and depression

OCD and depression can adversely impact your ability to function in a healthy way. Obsessions affect your state of mind. Compulsions can interfere with your schedule.

When your relationships, social life, therapy, and performance on the job or in school are affected, you may begin to experience symptoms of depression. Researchers have found that the more severe obsessions and compulsions are, the more they impact your daily functioning, worsening depression symptoms.

These two disorders share many overlapping symptoms, including:

  • They can affect your mood, relationships, and ability to function well.
  • Both are associated with negative beliefs about yourself.
  • They can cause thinking patterns that worsen symptoms.
  • Both can usually be improved with a combination of psychotherapy and medication – especially selective serotonin reuptake inhibitors (SSRIs).

Although OCD and depression share many symptoms, there are some critical distinctions.

  • OCD causes you to feel compelled to repeat certain behaviors to reduce anxiety, but depression does not usually involve repeating compulsive behaviors such as turning off and on light switches – though it is important to note that depression can be associated with compulsive use of alcohol, drugs, and sex.
  • OCD may cause tic disorders to develop, but there isn’t any research to suggest that tic disorders arise from depression.
  • Depression is classified as a mood disorder in the “Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5)”. In older versions of the DSM, OCD was classified as an anxiety disorder. In the DSM-5, OCD has been separated from both anxiety and mood disorders.

Though these two mental health conditions may be long lasting, they are both treatable.

First-line treatments such as medication and psychotherapy may make a big difference in the severity of OCD and depression symptoms.