Obsessive compulsive disorder - OCD treatment and therapy from NOCD

Obsessions vs. Delusions: What’s the Difference?

By Cody Abramson

Apr 14, 20236 minute read

Reviewed byPatrick McGrath, PhD

Obsessive-compulsive disorder (OCD) often involves unusual thoughts or beliefs. For example, people with the condition may feel they need to count something to a certain number or avoid thinking negative thoughts in order to ensure someone they care about isn’t harmed. 

The odd nature of these thoughts, along with how firmly they are sometimes believed, might make you wonder how they are different from delusions, like the ones that characterize disorders like schizophrenia. 

We spoke with Dr. Patrick McGrath, Chief Clinical Officer here at NOCD, to explore the relationship between obsession and delusions. Here’s what we learned.

What are obsessions in OCD?

Obsessions are persistent and recurring thoughts, images, and urges that are experienced involuntarily and cause significant distress. 

In some cases, obsessions take the form of unusual beliefs. Often, they involve ways to prevent harm, either to oneself or others, through means that are excessive or not related to the negative outcome in any plausible sense. Here are a few examples:

  • If I touch the remote with my left hand instead of my right, something terrible will happen to my spouse.
  • I need to think good thoughts when I walk into this room. Otherwise, I’ll come down with a severe illness.
  • If I tell others about the job I’m applying for, I won’t be offered the position.
  • I have to count the number of objects in my fridge five times, or it will all become contaminated.

While these thoughts involve bad outcomes, they clearly have nothing to do with them. But even though there’s no reason to believe that one’s negative thoughts could make them get sick, for example, doubt and fear in OCD can make these sorts of beliefs feel very real and urgent.

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What are delusions?

While there is no single, clear definition of delusions, there are some general traits that experts seem to agree to characterize these unusual beliefs. In particular, they highlight that delusions are:

  • Irrational: The core feature of delusions is that they are irrational. Specifically, they are not supported by evidence and do not change when contrary evidence is given. This is how the most recent edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V TR) defines delusions, stating that “delusions are fixed beliefs that are not amenable to change in light of conflicting evidence.”
  • Harmful: Some experts note that in addition to being irrational, delusions must also be physically or psychologically harmful. This helps to separate “ordinary” irrational beliefs from those that are clinically significant.
  • Misaligned with the beliefs of one’s group or culture: Even if there is inadequate evidence for someone’s fixed belief, we don’t want to call it a delusion when it is held by many members of one’s culture or other important groups they belong to. 

Though delusions can be about anything, most of them can be classified using six categories enumerated by the DSM. These include:

  • Persecutory delusions: These involve persistent and unjustified beliefs that one is going to be harmed by others or that others are out to get them
  • Referential delusions: The belief that ordinary events have hidden meanings that are related to the experiences of the individual with the delusion
  • Grandiose delusions: These are unfounded beliefs related to one’s wealth, power, identity, or overall importance
  • Erotomatic delusions: When someone believes, despite strong evidence to the contrary, that another person is in love with them
  • Nihilistic delusions: Characterized by an unjustified belief that some major catastrophe will occur
  • Somatic delusions: These are unshakeable beliefs that something is wrong with one’s body

How are obsessions and delusions distinguished?

With these descriptions in mind, delusions and obsessions can seem quite similar. They can both be irrational, harmful, and unsupported by the beliefs of one’s group or culture. With that said, there are a few key differences. 


The DSM separates individuals with OCD based on their level of insight, which refers to the degree to which they understand that their unusual beliefs are irrational. Dr. McGrath notes that “most people with OCD have a good to fair level of insight. The vast majority of people look at their OCD and say, logically, that they understand it doesn’t really make sense.” Because delusions generally involve sincere beliefs, with little to no awareness that they are irrational, insight is usually a reliable way to distinguish delusions from obsessions.


Obsessions are experienced as intrusive, meaning they are involuntary, unpleasant, and ego-dystonic, or misaligned with one’s genuine beliefs and values. When discussing delusions as they appear in schizophrenia, Dr. McGrath states, “you may not recognize these thoughts as intrusive,” In other words, they are less likely to be experienced as unwelcome or distressing representations of reality. This is not to say that delusions cannot cause distress, but that when they do, it’s generally not because they aren’t sincerely endorsed or believed. 

Responsiveness to counterevidence

Though delusions and obsessions are both irrational, those who experience obsessions are generally more responsive to counterevidence. For example, if an individual with OCD avoids engaging in their compulsions and comes to see that the bad events don’t occur, the strength of their obsessions and associated beliefs may reduce over time. Delusions, on the other hand, are defined by their resistance to counterevidence. 

Can obsessions turn into delusions?

Some individuals with OCD have no little to no insight about their obsessions. Specifically, one study found that while 50% of participants with OCD had high levels of insight, 15% had little or no insight. Dr. McGrath states that “when insight gets low enough, there’s a point at which it becomes delusion.”

However, Dr. McGrath emphasizes that it might not be helpful to call the person delusional or think of them as having some condition other than OCD. “As a clinician, I prefer not to use the term delusional,” he says. “Ultimately, my job is to work with these patients and potentially with other providers to see if there’s a way to help break that ‘delusional obsession,’ and terms like delusion don’t help us achieve this end.”  

Are obsessions and delusions treated differently?

Yes, obsessions and delusions require different treatments. The gold standard treatment for OCD is exposure and response prevention (ERP) therapy, where individuals confront their obsessions without engaging in compulsions in an attempt to alleviate anxiety or prevent bad outcomes. 

While the treatment has been found to be highly effective for OCD, Dr. McGrath notes that “it may not be as effective with someone who has the delusional level of belief in their obsession.” In that case, he notes that one may need to rely on a pharmacological intervention first. “One option is to go for a lower dose of an antipsychotic medication,” he says. “We have found that much lower doses are necessary to help convert a delusional obsession back into one with a low or fair level of insight. Then we can use ERP again.”

When delusions are not the result of OCD, like for people with schizophrenia, ERP may not be used at all unless there are compulsions or other behaviors associated with avoidance. In this case, physicians may rely primarily on higher doses of antipsychotics. However, talk therapy may still play a role in alleviating symptoms and helping patients develop better coping mechanisms. 

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