Ethnopharmacological relevance: Licorice preparations are used as neuroprotective remedies in Persian ethno-
medicine, in order to prevent from disabilities in neurodegenerative conditions like Parkinson's disease (PD).

Aim of the study: This study was designed to determine the licorice (root of Glycyrrhiza glabra L.) effectiveness as an adjunct treatment in the PD management.

Material and methods: In this double-blinded trial, 128 patients were assessed for eligibility criteria. Seventy-
eight patients were ineligible and 11 of them refused from participating. Thirty-nine PD patients (YAHR sta-
ging ≤ 3) were divided into two groups by random. The patients received oral licorice or placebo syrups with a dose of 5 cc, twice a day for 6 months. High-performance liquid chromatography and spectrophotometric in-
struments determined licorice syrup constituents. The patients' situation for Unified Parkinson's rating scale (UPDRS) was assessed every 6 weeks for the duration of six months. In addition, patients' blood pressure, blood
glucose, sodium and potassium levels, quality of life and dizziness were determined.
Results: Six weeks after intervention, total UPDRS, daily activities and tremor were significantly improved with a
considerable effect size. A significant better motor test and rigidity scores were observed 4 months after licorice
intake (p > 0.05). No electrolyte abnormality, significant changes in blood pressure or blood glucose levels were observed during the study. Each 5cc of syrup contained 136 mg of licorice extract with 12.14 mg glycyr-
rhizic acid, and also 136 μg of polyphenols.

Conclusion: The licorice intake could improve the symptoms in PD patients without serious adverse events.