Tourette syndrome is a childhood-onset neuropsychiatric disorder characterized by multiple motor and vocal tics that last for at least a year in duration. Currently, there exist several effective pharmacological treatments for childhood tics including alpha-2 agonist medications (guanfacine and clonidine) and neuroleptics (antipsychotic) medications. These medications, however, have significant side-effects and are only partially efficacy in treating tics.

N-acetylcysteine (NAC) is a natural supplement that acts as an antioxidant and glutamate modulating agent. NAC has been used safely for decades in doses 20-40 times higher than in this trial as an antidote for acetaminophen overdose. The only side-effect commonly seen with NAC is nausea and this side-effect is seldom seen in the doses used in this trial.

NAC has recently been demonstrated to be effective in a double-blind, placebo-controlled trial in adults with trichotillomania (chronic hair pulling). Hairpulling is hypothesized to be closely related to tics because these conditions (1) have similar clinical characteristics -- both groups typically experience urges before engaging in pulling or tics, (2) neuroimaging studies suggest they involve similar brain circuits -- the basal ganglia, (3) the same pharmacological treatments (neuroleptics) may be effective for both conditions and (4) they tend to be inherited together in families. In other trials NAC has evidence of some efficacy in treating diverse psychiatric conditions such as bipolar depression, schizophrenia and cocaine dependence.

The investigators are conducting this trial to determine if NAC is an effective treatment for tics.

Inclusion Criteria:

• Children aged 8-17 years.
• Primary diagnosis of Tourette syndrome or chronic tic disorder.
• Duration of tics greater than 1 year.
• Significant Current tic symptoms: Current YGTSS score greater than or equal to 22 with a TS diagnosis or greater than or equal to 14 with a chronic tic disorder.

Exclusion Criteria:

• Comorbid bipolar disorder, psychotic disorder, substance use disorder, developmental disorder or mental retardation (IQ<70).
• Recent change (less than 4 weeks) in medications that have potential effects on tic severity (such as neuroleptic medications, dopamine agonists, alpha-2 agonists (guanfacine, clonidine or prazosin), SSRIs, clomipramine, naltrexone, lithium, psychostimulants, or anxiolytics). Medication change is defined to include dose changes or medication discontinuation.
• Recent change in behavioral treatment for Tourette syndrome or comorbid conditions (i.e. OCD) within the last 4 weeks or initiation of behavioral therapy for tics within the last 12 weeks.
• Asthma requiring medication use within the last 3 months
• Known hypersensitivity or previous anaphylactoid reaction to acetylcysteine or any components in its preparation
• Positive pregnancy test or drug screening test.
• Previous use of N-acetylcysteine (dose greater than 600mg for more than 2 weeks)

Every 4 weeks until the completion of the 12-week study

Adverse events were systematically assessed with every assessment using the PAERS, unless they were brought to our attention by the subject between assessment periods.