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What causes unwanted intrusive thoughts?

Unwanted intrusive thoughts are sudden, repetitive thoughts, images or impulses that are disturbing or distressing. They seem to come from “out of the blue” and cause significant anxiety or distress. Intrusive thoughts can range from mildly unpleasant to extremely disturbing, violent or traumatic. They often go against a person’s values and can be very worrying. Almost everyone experiences some form of intrusive thoughts at some point, but when they become persistent, extreme or distressing, it may signal an underlying condition that requires treatment. This article explores the common causes and origins of unwanted intrusive thoughts.

What are intrusive thoughts?

Intrusive thoughts are involuntary thoughts or images that seem to become “stuck” and repeat against our will and desires. Some examples include:

  • Violent or horrific images (e.g. picturing hurting a loved one)
  • Sexual thoughts or images of a disturbing nature
  • Blasphemous or sacrilegious thoughts
  • Thoughts of harming yourself
  • Doubts about your relationships, such as questioning your love for your partner
  • Concerns about illness, contamination or disaster

Intrusive thoughts often cause strong negative feelings like fear, disgust, doubt, guilt or shame. Most people experience odd or inappropriate thoughts at some point, but they are able to dismiss them. However, for some people, these thoughts are very disturbing and difficult to manage. The feeling that the thoughts are uncontrollable can cause a lot of distress.

What causes intrusive thoughts?

There are a few key factors that are thought to cause unwanted intrusive thoughts:

Anxiety disorders

Anxiety disorders like obsessive compulsive disorder (OCD), generalized anxiety disorder (GAD) and post-traumatic stress disorder (PTSD) have been strongly linked to intrusive thoughts. When someone has an anxiety disorder, their brain becomes hyper-reactive. Minor stresses trigger a dramatic “fight or flight” response, flooding the brain with anxiety and stress hormones. This hyper-reactivity makes neutral stimuli seem dangerous or worrying. Harmless thoughts begin to take on inflated importance and trigger spikes of fear and distress.

With OCD specifically, the intrusive thoughts themselves become the main object of anxiety. The disorder centers around repeated obsessive thoughts and their associated compulsive behaviors. Common OCD obsessions that involve intrusive thoughts include:

  • Fear of contamination or illness
  • Harming others
  • Causing harm by accident (e.g. hitting someone while driving)
  • Horrific or violent imagery
  • Doubting relationships
  • Concern with sacrilege or blasphemy

People with OCD experience these intrusions frequently and profoundly. The repetitive OCD cycle leads to increased frequency and intensity of intrusive thoughts over time.


Past trauma and PTSD are also linked to intrusive thoughts, which may take the form of involuntary flashbacks. A person who went through a traumatic event may involuntarily re-experience vivid memories, images or sensations related to the trauma. These intrusions are very distressing and difficult to control. Sexual assault survivors, combat veterans and victims of abuse often struggle with intrusive thoughts related to their trauma.


Depression has also been associated with more frequent and disturbing unwanted thoughts. People with depression tend to experience more negative rumination – repetitive thinking about the causes, meaning and consequences of their depressive symptoms. They may become preoccupied with intrusive thoughts about guilt, failure, death, or their own flaws and shortcomings.

Sleep deprivation

Lack of sleep can contribute to intrusive thoughts. When people are very sleep-deprived, the rational control centers of their brain lose some power. This makes it harder to regulate thoughts and emotions. Strange thoughts and images may spontaneously arise due to the brain being in an uncontrolled, disinhibited state. Many people experience odd, vivid thoughts as they are falling asleep for similar reasons.

Drug use

Using recreational drugs, particularly hallucinogens like LSD, can also lead to disturbing intrusive thoughts. The drugs cause dramatic changes in brain function that lead to loss of control over thoughts, emotions and perceptions. This allows bizarre thoughts and imagery to spill forth unchecked. These drug-induced intrusions often cause great distress.

Brain injury or illness

Damage to certain areas of the brain has also been linked to intrusive thoughts. Injuries, tumors, dementia and other brain disorders can impair the brain’s ability to control thoughts and behaviors. This lack of control can open the floodgates to unwanted thoughts.

Why are some thoughts intrusive or disturbing?

Most people have odd or disturbing thoughts pass through their minds at some point. But some thoughts become intrusive or distressing due to:

  • How frequently they occur
  • How vivid or graphic they are
  • How violent, horrific or sexual the content is
  • How greatly they clash with the person’s values

Thoughts that center around our deepest fears, doubts and repressed desires tend to have the most power and impact. Intrusive thoughts also gain power from the great distress and shame they evoke. The more energy we give them, the more intrusive they become. Attempts to suppress intrusive thoughts often makes them worse, as suppression draws more attention to them.

Why do they feel uncontrollable?

Intrusive thoughts can feel impossible to control for several reasons:

  • They tend to spike when we are stressed, tired or distracted, reducing mental control
  • They often represent underlying fears or doubts we are afraid to face
  • Trying to repress them can backfire and give them more power
  • Anxiety disorders like OCD have biological roots that make thoughts FEEL unmanageable

In reality, intrusive thoughts respond very well to therapeutic techniques teaching acceptance rather than suppression and control. Learning to allow intrusive thoughts to flow through our mind without reaction can dramatically reduce their intensity and frequency. They become much less “sticky” and no longer represent deep unconscious fears.

Are intrusive thoughts normal?

Mild or passing intrusive thoughts are very common and do not indicate any mental disorder. Studies suggest around 94% of people experience odd intrusive thoughts. However, when intrusive thoughts are very disturbing, repetitive, uncontrollable and distressing, they can signify issues like OCD, PTSD or severe anxiety needing treatment.

Some key characteristics of normal vs. abnormal intrusive thoughts:

Normal intrusive thoughts Abnormal intrusive thoughts
Brief, passing Persistent, recurring frequently
Not too disturbing Extremely disturbing content
Don’t clash too strongly with values Greatly clash with personal values
Don’t cause extreme distress Cause severe anxiety, disgust, guilt
Person can dismiss thoughts Feel impossible to dismiss or control
Don’t severely impair functioning Impair work, relationships, life activities

What conditions are linked to intrusive thoughts?

Frequent and disturbing intrusive thoughts may be a sign of:

Obsessive-compulsive disorder (OCD)

OCD causes repeated obsessions and mental rituals. Obsessions are recurring intrusive thoughts that generate fear and anxiety. Common obsessions include contamination fears, violent or horrific images, doubts about relationships, and unacceptable sexual thoughts. Mental rituals like counting or mentally reviewing events are used to reduce anxiety and dismiss the thoughts.

Generalized anxiety disorder (GAD)

GAD involves chronic, exaggerated worry about everyday events. Intrusive thoughts about possible threats, future disasters and doubts about relationships are common. The relentless worrying is very distressing but difficult to control.

Post-traumatic stress disorder (PTSD)

Reliving a traumatic event through vivid, intrusive memories is a core symptom of PTSD. The involuntary “flashbacks” contain traumatic sensory details like sounds, smells, images, or sensations. They feel like a recurring replay of the trauma against the person’s will.

Major depression

Depression is characterized by constant negative, self-critical rumination. Depressive intrusive thoughts often focus on guilt, failure, hopelessness or death. The inability to stop dwelling on these thoughts contributes greatly to the emotional pain of depression.

Bipolar disorder

During manic episodes, people with bipolar disorder may experience racing thoughts, distractibility, and flights of ideas. The fast unpredictable thoughts feel out of control. Some thoughts may also be bizarre or delusional.


Schizophrenia causes hallucinations – hearing voices or seeing things that are not there. These hallucinations are involuntary, disturbing and feel uncontrollable, much like intrusive thoughts. However, hallucinations seem completely real to the person.

Drug use

Hallucinogenic drugs like LSD, ketamine, and certain designer drugs can all cause frightening intrusive thoughts and distorted thinking. These thoughts arise from the brain’s neurochemical imbalances caused by ingesting the drugs.

What makes intrusive thoughts worse?

Certain factors can make intrusive thoughts more frequent and distressing:

Focusing on the thoughts

Paying too much attention to intrusive thoughts fuels them. Our thoughts tend to follow where we direct our focus. Getting locked into a battle against bad thoughts gives them energy and persistence.

Trying to suppress thoughts

Pushing intrusive thoughts out of conscious awareness often backfires. Suppressing thoughts requires focusing our attention on them, which makes them seem more prominent. They tend to keep popping back up as the mind checks if they are still suppressed.

Avoiding triggers

While avoiding obvious triggers like horror movies may help, avoiding normal life activities out of fear of triggering thoughts just increases anxiety and obsession. The thoughts get attached to more and more harmless things.

Seeking reassurance

Asking others for reassurance that intrusive thoughts are “normal” or “don’t count” can provide temporary relief. But it also gives the thoughts undeserved significance. It communicates they are something that requires reassuring words from others.

Mental review and “undoing”

Mentally reviewing thoughts to “cancel them out” keeps them front and center. Trying to “undo” thoughts through compulsive behaviors makes them seem more real and powerful.

Judging and reacting to thoughts

Thoughts gain power from our emotional reactions to them. Feeling guilt, disgust and shame about intrusive thoughts means we have given them authority they don’t deserve. This fuels the cycle.

How are intrusive thoughts treated?

Treatment focuses on decreasing the frequency and associated distress of intrusive thoughts rather than eliminating them entirely. Some effective therapies and treatments include:

Cognitive behavioral therapy (CBT)

CBT helps people relate to intrusive thoughts differently by reducing fear and judgment of them. Exposure therapy encourages gradual exposure to triggering thoughts and images until they no longer provoke anxiety.

Acceptance and commitment therapy (ACT)

ACT teaches people to accept and detach from intrusive thoughts and urges through mindfulness. This stops fueling the obsessional cycle.

Exposure and response prevention (ERP)

ERP is commonly used for OCD intrusions. People are exposed to thoughts deliberately while refraining from compulsive rituals, so the thoughts lose their power.


Antidepressants like SSRIs and SNRIs are commonly used to treat anxiety and OCD. They may reduce the frequency and intensity of intrusive thoughts.

Transcranial magnetic stimulation (TMS)

TMS uses magnetic pulses to activate underactive parts of the brain linked to impulse control and cognitive regulation. It has shown promise for reducing OCD symptoms.

Treatment focuses less on the content of the thoughts and more on their repetitive, uncontrollable quality. The key is accepting that we can’t fully control what comes into our minds. Intrusive thoughts only have as much power as we give them through our reactions.


Frequent and disturbing intrusive thoughts are often a sign of an underlying issue like OCD, PTSD or anxiety needing compassionate treatment. While intrusive thoughts may feel uncontrollable, they can be managed using CBT, ERP, ACT, medication and mindfulness approaches. Rather than struggling to control or eliminate them, treatment helps people relate to these thoughts differently, which removes their impact and intensity. This helps restore a sense of control.