Media portrayal:


Scientific interpretation:

Small study investigates NAC – but what about the placebo effect?

Original article: N-Acetyl Cysteine Is Associated With Dopaminergic Improvement in Parkinson’s Disease, Clin Pharmacol Ther: May 24, 2019.

The takeaway

A small study without blinding or a placebo arm has shown benefits from oral and intravenous NAC.

Impact Opinion

“Again, evidence accumulates to support the trial of candidates selected by its LCT committee but struggling to find funding because of their limited or absent commercial potential; this time N-acetyl cysteine (NAC).

Although this is a small study with only short-term outcomes, it further corroborates evidence accumulated by CPT to date of its potential utility in PD. NAC is currently approved for the treatment of mucus secretions in pulmonary disease and the treatment of acetaminophen (Paracetamol) overdose. NAC is also available universally as a non-regulated nutritional supplement.”


Oxidative stress is damaging to neurons, and reducing its effects forms the rationale behind investigating the effects of N-acetyl cysteine, or NAC. NAC is used in a variety of clinical situations, including paracetamol overdose, as it helps replace cellular glutathione, involved in reducing harmful oxidative stress.

Based on previous findings in animal models as well as investigations in humans, the team ran a study addressing the effects of oral and intravenous NAC in people with Parkinson’s, to address whether it could have a beneficial effect.

The details

Forty two people with Parkinson’s were enrolled in the study, 28 of whom were assigned to NAC treatment, and 14 to the control group. Over a period of 3 months, NAC was infused intravenously over approximately 1 hour, once per week. On the rest of the days, participants took NAC tablets twice a day. Importantly, the control group did not receive a placebo, and the NAC group were not blinded, that is, they were aware of the drug they were taking.

All participants underwent a baseline neurological assessment, which was repeated after 90 days. They also underwent brain scanning at the start and end of the study, to get a quantitative measure of changes in the dopamine and serotonin functioning.

The researchers found that the NAC group showed a 4 point improvement on their UPDRS scores, reflecting changes in both motor and non-motor function, while the control group did not. In addition, analysis of the brain scans revealed some increases in dopamine and serotonin transport in key brain areas linked to movement.

Next steps

These results are unfortunately hampered by the lack of a placebo control – in other words, the UPDRS improvements seen may have been due to a placebo effect, which is known to be robust in people with Parkinson’s.

In addition, blinding is necessary, to ensure that for the duration of the study neither participant nor researcher are aware of what treatment (drug or placebo) is being given to an individual, to avoid any bias or influence on the results. Future studies in the format of a placebo controlled, double blinded trial are necessary in order to establish the true therapeutic potential of NAC for Parkinson’s.

Original article: Monti DA, Zabrecky G, Kremens D, Liang TW, Wintering NA, Bazzan A J, Newberg AB. May 24, 2019. N-Acetyl Cysteine Is Associated With Dopaminergic Improvement in Parkinson’s Disease


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