Study of Dextromethorphan in OCD and Related Disorders

May 18, 2026 updated by: Peter J van Roessel, MD PhD, Stanford University

Fluoxetine/Dextromethorphan in Obsessive-Compulsive and Related Disorders: an Open-Label Crossover Pilot Study

The purpose of the study is to assess the tolerability and efficacy of dextromethorphan in combination with fluoxetine for symptom relief in OCD and related disorders.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

Obsessive compulsive disorder (OCD) and the related disorders body dysmorphic disorder (BDD), somatic symptom disorder (SSD) and illness anxiety disorder (IAD) are psychiatric conditions characterized by recurrent, intrusive thoughts, feelings or images (obsessions or preoccupations) and repetitive or ritualized behaviors or avoidance performed to relieve obsession or preoccupation-related anxiety. They are a significant cause of mental health-related disability, and are inadequately served by available treatments.

This study tests whether an over-the-counter cough suppressant medicine, dextromethorphan, may offer symptom relief when combined with a low dose of fluoxetine, a standard prescription treatment for OCD and related disorders.

Study Type

Interventional

Enrollment (Estimated)

60

Phase

  • Phase 2

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • United States
    • California
      • Stanford, California, United States, 94304
        • Recruiting
        • Stanford University
        • Principal Investigator:
          • Peter van Roessel, MD, PhD
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years to 65 years (Adult, Older Adult)

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Diagnosis of obsessive-compulsive disorder (OCD), body dysmorphic disorder (BDD), illness anxiety disorder (IAD) or somatic symptom disorder (SSD)
  • Living within California
  • Capacity to provide informed consent

Exclusion Criteria:

  • Current bipolar disorder or psychotic disorder
  • Active moderate or severe substance use disorder, lifetime severe substance use disorder
  • Pregnant or nursing women
  • Use of prescribed psychotropic medications other than fluoxetine for 2 weeks prior to study start
  • Having commenced OCD-targeted exposure and response-prevention (ExRP) psychotherapy within 2 months of study start

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Single

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Group A: fluoxetine then fluoxetine plus dextromethorphan
Group A participants will take fluoxetine 20mg (or prior dose) daily for 4 weeks, and will then continue fluoxetine while adding over the counter dextromethorphan, with doses increasing weekly as tolerated, for 4 weeks.
Drug: Fluoxetine
Fluoxetine 20mg (or previously prescribed dose) will be taken once daily by mouth for 8 weeks
Other Names:
  • Prozac
Drug: Dextromethorphan
Dextromethorphan, an over-the-counter cough suppressant, will be taken by mouth twice daily for four weeks of the study, starting at 15mg per dose, and increasing weekly as tolerated to a maximum of 60mg per dose.
Experimental: Group B: fluoxetine plus dextromethorphan then fluoxetine
Group B participants will take fluoxetine 20mg (or prior dose) daily together with over the counter dextromethorphan, with doses increasing weekly as tolerated, for 4 weeks, and then will stop dextromethorphan, continuing fluoxetine alone for 4 weeks.
Drug: Fluoxetine
Fluoxetine 20mg (or previously prescribed dose) will be taken once daily by mouth for 8 weeks
Other Names:
  • Prozac
Drug: Dextromethorphan
Dextromethorphan, an over-the-counter cough suppressant, will be taken by mouth twice daily for four weeks of the study, starting at 15mg per dose, and increasing weekly as tolerated to a maximum of 60mg per dose.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Improvement in OCD or related disorder symptoms as measured by the Y-BOCS
Time Frame: Change from baseline will be assessed at 4 weeks and at 8 weeks.
Improvement in OCD severity is measured by the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), a gold standard measure of the severity of obsessions and compulsions. Variants of the Y-BOCS designed for assessment of body dysmorphic disorder or illness anxiety disorder/somatic symptom disorder will be used as appropriate. Y-BOCS scores range from 0 to 40, with higher scores indicating greater severity of symptoms. Response will be defined as a 35% reduction in Y-BOCS score.
Change from baseline will be assessed at 4 weeks and at 8 weeks.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Improvement in clinical insight as measured by the BABS
Time Frame: Change from baseline will be assessed at 4 weeks and at 8 weeks.
Improvement in clinical insight is measured by the Brown Assessment of Beliefs Scale (BABS), a scale assessing multiple dimensions of clinical insight as relevant to OCD and related disorders. The BABS rates multiple dimensions of clinical insight related to an identified belief. BABS scores range from 0-24, with higher scores indicating greater insight impairment. Response will be defined as a 35% reduction in BABS score.
Change from baseline will be assessed at 4 weeks and at 8 weeks.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Stanford University

Collaborators

Avy L. & Roberta L. Miller Foundation

Investigators

  • Principal Investigator: Peter J van Roessel, MD PhD, Stanford University

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

January 20, 2022

Primary Completion (Estimated)

April 1, 2027

Study Completion (Estimated)

December 1, 2028

Study Registration Dates

First Submitted

May 13, 2021

First Submitted That Met QC Criteria

May 20, 2021

First Posted (Actual)

May 24, 2021

Study Record Updates

Last Update Posted (Actual)

May 20, 2026

Last Update Submitted That Met QC Criteria

May 18, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 60569

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

Yes

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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