Table 2.

Clinical Trials Investigating Modulation of the Microbiota-Gut-Brain Axis in Health and Neurodegenerative Diseases With Selected Medicinal Herbs.

Disease state	N	Treatment	Duration	Assessment	Effects compared to placebo	Ref.
Memory impaired elderly	40	250 mg Bacopa monnieri extract or placebo	12 weeks	Cognition and memory	Treatment increased mental control, logical memory and paired associated learning	128
Healthy elderly	98	300 mg B. monnieri extract or placebo	12 weeks	Memory and learning	Treatment improved verbal learning, memory acquisition, and recall.	130
Healthy elderly	60	300 mg B. monnieri extract or placebo	12 weeks	Cognition, memory, and neurotransmitter activity	Treatment improved attention, cognitive processing, working memory, and reduced acetylhydrolase activity	106
Healthy elderly	48	300 mg B. monnieri extract or placebo	12 weeks	Cognition, memory, and mood	Treatment improved memory and attention; scores of anxiety, depression and heart rate decreased	131
Senile dementia of Alzheimer’s type patients	201	1,000 mg B. monnieri (whole plant), Hippophae rhamnoides (leaves and fruits) and Dioscorea bulbifera (bulbils) or 20 mg donepezil drug (Aricept)	12 months	Cognition, memory, and mood	Treatment improved markers of inflammation, oxidative stress and cognition which included MMSE, word recall, attention span, functional activity and depression scores	166
Mild cognitive impairment	50	600 mg/day Withania somnifera root extract or placebo	8 weeks	Cognition and memory	Treatment improved memory, executive function, focused attention, and information-processing speed	174
Cognitive dysfunction in bipolar disorder	53	500 mg/ day W. somnifera root extract or placebo	8 weeks	Cognition and memory	Treatment improved auditory-verbal working memory, reaction time, and social cognition	175
Parkinson’s Disease	23	40-50 g Mucuna pruriens (4.5-5.5% L-Dopa) per day	4 weeks	Efficacy and tolerability of M. pruriens	Treatment improved motor scores and treatment was tolerated	142
Parkinson’s Disease	60	7.5 g HP-200 (4% L-Dopa) from M. pruriens	12 weeks	Efficacy and tolerability of HP-200 derived from M. pruriens	Treatment reduced Hoehn and Yahr stage and UPDRS scores; mild adverse events	143
Parkinson’s Disease	8	15 g or 30 g M. pruriens, or levodopa/carbidopa control	1 dose	Motor symptoms and pharmacokinetics	Compared to conventional drug therapy, 30 g mucuna led to faster onset of effect with shorter latencies to peak L-dopa plasma concentrations, longer on time, and higher peak L-dopa plasma concentration	154
Parkinson’s Disease	2	200 mg M. pruriens extract after conventional drug washout	2 doses	Kinetic-dynamic comparison case study	Impaired L-dopa bioavailability after M. pruriens administration	156
Parkinson’s Disease	18	17.5 mg/kg M. pruriens, 12.5 mg/kg M. pruriens, Mucuna with DCCI, levodopa control, levodopa plus DCCI control or placebo	1 dose	Motor and cardiovascular parameters	Low dose M. pruriens promoted fewer dyskinesias and adverse events compared to drug control; high dose M. pruriens promoted better motor response, longer on time, fewer dyskinesias, and fewer adverse events compared to drug control; cardiovascular parameters were unchanged	155
Parkinson’s Disease	14	M. pruriens dosage based on patients’ levodopa dosage	16 weeks	Efficacy and tolerability of M. pruriens	Treatment response was similar to drug response on all efficacy measures	153
Healthy elderly subjects	28	250 to 750 mg Centella asiatica extract/day or placebo	8 weeks	Memory and mood	Treatment improved working memory and mood	176