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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Date results information initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
N-acetyl cysteine (NAC) augmentation in Obsessive-Compulsive Disorder (OCD): A 24-week, randomized, double blind placebo controlled trial
Scientific title
N-acetyl cysteine (NAC) augmentation in Obsessive-Compulsive Disorder (OCD): A 24-week, randomized, double blind placebo controlled trial
Secondary ID [1] 289527 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Obsessive-Compulsive Disorder 299233 0
Condition category
Condition code
Mental Health 299243 299243 0 0
Other mental health disorders

Study type
Description of intervention(s) / exposure
The amino acid N-acetyl cysteine (NAC; 500mg per capsule, taken orally) or placebo (capsules containing microcellulose), used adjunctive to stable medication (minimum 8-weeks at consistent dosages) for 24 weeks in adults (18-75 years of age) with OCD.

Randomised participants will take 2 capsules, twice per day (equating to 2,000mg NAC or placebo per day) for the first 8-weeks of the study. However, the dose of NAC (or placebo) may increase from the week-8 visit. In cases of non-response (<35% reduction in baseline score of primary outcome measure: Y-BOCS), participants will increase their dose by an additional 1,000mg per day (3 capsules taken orally twice per day; equating to 3,000mg NAC or placebo per day) from week-8 and remain on this dose for the following 4-weeks. If the participant continues to be non-responsive at the week-12 visit, an additional 1,000mg may be added (4 capsules taken orally twice per day).

The maximum dose permitted in this study will be 4,000mg per day, however, participants will only be permitted to increase their dose by 1,000mg (per day) at a time and must remain on this dose for a minimum of 4-weeks before further titration can occur. Titration may occur at week-8, week-12, week-16 and week-20 in cases of non response. If the participant has reported any side effects/adverse events, titration will only occur if deemed suitable by the medical investigators.

Participants will be asked to return all remaining capsules in their containers at each study follow-up visit. Remaining capsules will be counted by a 3rd party to determine participant compliance.
Intervention code [1] 295119 0
Treatment: Drugs
Comparator / control treatment
Placebo capsules containing microcellulose
Control group

Primary outcome [1] 298725 0
Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), clinician administrated (severity scale Q1-Q10 and insight Q11)
Timepoint [1] 298725 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [1] 325064 0
Structured Interview Guide for the Hamilton Depression Rating Scale (HAM-D; 17-item), clinician administrated
Timepoint [1] 325064 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [2] 325068 0
Beck Anxiety Inventory (BAI), self-reported
Timepoint [2] 325068 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [3] 325069 0
Sheehan Disability Scale (SDS), self-reported
Timepoint [3] 325069 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [4] 325070 0
World Health Organisation Quality of Life Brief (WHOQOL-bref), self-reported
Timepoint [4] 325070 0
Baseline, Week-12, Week-20
Secondary outcome [5] 325071 0
Clinical Global Impression Scale (CGI), clinician administrated
Timepoint [5] 325071 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [6] 325072 0
Participant Global Impression scale (PGI), self-reported
Timepoint [6] 325072 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [7] 325074 0
Barratt Impulsivity Scale
Timepoint [7] 325074 0
Baseline only, used as a predictor of response/non-response
Secondary outcome [8] 325076 0
Dietary Questionnaire for Epidemiological Studies version 3.2
Timepoint [8] 325076 0
Baseline only
Secondary outcome [9] 325077 0
Systematic Assessment for Treatment Emergent Events (SAFTEE), self reported.

NAC may induce gastrointestinal side effects including mild abdominal pain or discomfort, heartburn, diarrhea, flatulence, nausea and cramps. Headaches and skin rashes have also been reported in previous clinical studies. However, specific to psychiatric research studies, only a small minority of participants have withdrawn due to side effects of NAC including a skin rash (n = 1), aggression (n = 1), severe heartburn (n = 1), neutropenia with 6 grams of NAC which resolved when dose reduced to 2.4g, (n = 1) and sensorineural deafness (n = 1) (Slattery et al., 2015).
Timepoint [9] 325077 0
Week-4, Week-8, Week-12, Week-16, Week-20, Week-24
Secondary outcome [10] 347744 0
Dimensional Obsessive Compulsive Scale (DOCS) - self-reporting
Timepoint [10] 347744 0
Baseline, Week-4, Week-8, Week-12, Week-16, Week-20, Week-24

Key inclusion criteria
Primary diagnosis of OCD as per the Structured Interview Guide for the DSM-5 (SCID)
Adults between the age of 18-75 who have the desire and capacity to consent to the study and follow its procedures.

Minimum score of 16 on the Y-BOCS at time of entry into the study, but no greater than 31.

Currently taking medication for their OCD which has been at a stable dose for the past 8-weeks.

Stable psychological treatment (if employing) for minimum eight weeks (an 8-week wash-out period will be required if participants have just completed an intensive in-patient CBT program for their OCD).
Minimum age
18 Years
Maximum age
75 Years
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
*Bipolar disorder
*Psychotic disorders
*Primary diagnosis of Obsessive-compulsive spectrum disorders including hoarding, body dysmorphic disorder, trichotillomania (secondary diagnosis permitted)
*Severe depression (as defined by HAM-D score equal to or greater than 24
*Alcohol/substance abuse
*Y-BOCS score equal to or greater than 32
*Treatment resistant OCD (3 or more trials of first line medications for their OCD at therapeutic doses for minimum of 12-weeks each, at least one augmentation strategy, for example, anti psychotic medication as well as exposure response prevention therapy minimum 20 hours)
*Medications with known or suspected negative interactions with NAC (activated charcoal, nitro glycerine, insulin replacement therapies, Aralen, anti-coagulant medications excluding aspirin and NSAIDS)

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Randomisation of participants to treatment groups will be determined by computerised random allocation. Recruited eligible participants will be assigned a participant number and provided capsules according to a corresponding investigational product (IP) number. Participant numbers are provided sequentially and the randomisation code is set up in a 2 by 2 block design, with no group identifying them (to avoid potentially unblinding researcher’s if participants were randomised to medication bottles labelled A or B).
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s
The people administering the treatment/s
The people assessing the outcomes
The people analysing the results/data
Intervention assignment
Other design features
Participants will be randomised into either NAC or placebo in a double blind manner.
Phase 3
Type of endpoint/s
Statistical methods / analysis
The study will be powered to detect a post-treatment difference of at least 3 points on the primary measure (YBOCS) between groups (NAC/placebo). As the outcome of interest will be a treatment * time interaction, the effect size of interest is then the magnitude of that interaction term estimate. As the trial involves 7 assessments (6 post-baseline), In order to reach the specified treatment effect (3 point relative reduction on the YBOCS), YBOCS score would need to be reduced at a mean of 0.5 points greater in the active group than the placebo group at each post-baseline visit. As such, the minimum effect size of the interaction term is 0.5. The sample size required to achieve this effect size with 80% power can be accurately assessed by applying Monte Carlo simulation (with 1000 simulations) to the data that is available from the pilot trial. Results of the power analysis revealed that with a sample of 128 (64 per treatment arm) the trial will be powered at 80% (95% CI: 80.4, 85.2).

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment hospital [1] 6014 0
The Melbourne Clinic - Richmond
Recruitment hospital [2] 6015 0
Royal Brisbane & Womens Hospital - Herston
Recruitment postcode(s) [1] 24712 0
2145 - Westmead
Recruitment postcode(s) [2] 13441 0
3121 - Richmond
Recruitment postcode(s) [3] 13442 0
4001 - Brisbane

Funding & Sponsors
Funding source category [1] 293903 0
Government body
Name [1] 293903 0
The National Heath and Medical Research Council
Country [1] 293903 0
Primary sponsor type
The University of Melbourne
Melbourne VIC
Australia, 3052
Secondary sponsor category [1] 292728 0
Name [1] 292728 0
The University of Queensland
Address [1] 292728 0
St Lucia
QLD 4072
Country [1] 292728 0
Secondary sponsor category [2] 295732 0
Name [2] 295732 0
Western Sydney University
Address [2] 295732 0
Western Sydney University
Westmead Campus
158-160 Hawkesbury Rd
Westmead, NSW, 2145
Country [2] 295732 0

Ethics approval
Ethics application status
Ethics committee name [1] 295320 0
The Melbourne Clinic Research Ethics Committee
Ethics committee address [1] 295320 0
2 Salisbury St,
VIC 3121
Ethics committee country [1] 295320 0
Date submitted for ethics approval [1] 295320 0
Approval date [1] 295320 0
Ethics approval number [1] 295320 0
Ethics committee name [2] 297979 0
Western Sydney University Human Research Ethics Committee
Ethics committee address [2] 297979 0
Penrith Campus
Great Western Highway
NSW 2747
Ethics committee country [2] 297979 0
Date submitted for ethics approval [2] 297979 0
Approval date [2] 297979 0
Ethics approval number [2] 297979 0
Ethics committee name [3] 297980 0
UQ Medical Research Ethics Committee (MREC)
Ethics committee address [3] 297980 0
University of Queensland (UQ)
Level 3, Brian Wilson Chancellery
The University of Queensland
St Lucia QLD 4072, Australia
Ethics committee country [3] 297980 0
Date submitted for ethics approval [3] 297980 0
Approval date [3] 297980 0
Ethics approval number [3] 297980 0

Brief summary
This study seeks to elucidate the benefits of NAC augmentation (2-4 grams/day) compared to placebo in the treatment of OCD, in a 24-week, multi-centre, randomized, double-blind, placebo controlled trial. It is hypothesized that NAC will be superior over placebo for improving OCD symptoms as measured by a reduction in Y-BOCS scores from baseline against each subsequent time point (W4, W8, W12, W16, W20 and W24). Additional benefits are anticipated for relieving anxiety as well as improving mood, functioning and overall quality of life.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 66874 0
Prof Jerome Sarris
Address 66874 0
The Melbourne Clinic Professorial Unit
2 Salisbury St,
Melbourne VIC 3121
Country 66874 0
Phone 66874 0
+61 3 94874748
Fax 66874 0
Email 66874 0
Contact person for public queries
Name 66875 0
Georgina Oliver
Address 66875 0
The Melbourne Clinic Professorial Unit
2 Salisbury St,
Melbourne VIC 3121
Country 66875 0
Phone 66875 0
+61 3 8344 0189
Fax 66875 0
Email 66875 0
Contact person for scientific queries
Name 66876 0
Georgina Oliver
Address 66876 0
The Melbourne Clinic Professorial Unit
2 Salisbury St,
Melbourne VIC 3121
Country 66876 0
Phone 66876 0
+61 3 83440189
Fax 66876 0
Email 66876 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
What data in particular will be shared?
-Participant data supporting the publication results
-Participant data relating to primary outcomes
-Participant safety data
When will data be available (start and end dates)?
Data are available straight after publication for an indefinite time
Available to whom?
Data are potentially available to researchers who have obtained ethics approval from a registered HREC to conduct their research. All other data sharing proposals will be assessed on a case by case basis by the study investigators.
Available for what types of analyses?
HREC approved study protocols and IPD meta-analysis or systematic reviews. Other analysis requests will be assessed on a case by case basis by the study investigators.
How or where can data be obtained?
Access can be requested via the Health Data Australia catalogue (https://researchdata.edu.au/health). Search for the ACTRN number in the catalogue to find datasets associated with this trial.

What supporting documents are/will be available?

Doc. No.TypeCitationLinkEmailOther DetailsAttachment
256Study protocol    370954-(Uploaded-19-03-2024-17-15-09)-Study-related document.pdf
22305Data dictionary    370954-(Uploaded-19-03-2024-17-39-14)-Study-related document.pdf

Results publications and other study-related documents

Documents added manually

Documents added automatically
No additional documents have been identified.