May 7, 2014

Effect of Ashwagandha on Tests of Cognitive and Psychomotor Performance

Review of a prospective, double-blind, multi-dose, placebo-controlled, crossover study
This study evaluated the effects of ashwagandha (Withania somnifera) on cognitive and psychomotor performance in healthy human participants. After 14 days of treatment with the herb, outcomes showed significantly improvement and no sedative effects.


Pingali U, Pilli R, Fatima N. Effect of standardized aqueous extract of Withania somnifera on tests of cognitive and psychomotor performance in healthy human participants. Pharmacognosy Res. 2014;6(1):12-18.


A prospective, double-blind, multi-dose, placebo-controlled, crossover study with participants randomized to receive either Withania somnifera or placebo in Run I. A washout period of 14 days was given between Run I and Run II. All test procedures were repeated pre- and post-treatment for Run I and Run II. After 2 weeks of intervention, compliance was evaluated by questioning the subjects and counting any capsules left over.


26 healthy males, aged 20–35 years old were screened. Subjects were excluded if there was any evidence of physical illness, drug abuse, or aberrant laboratory findings when screened. Twenty participants completed the study.

Study Medication and Dosage

Randomized to 2 caps twice a day, morning and evening, of Withania or placebo.

250 mg capsules of standardized aqueous extract of the roots and leaves of Withania somnifera (SENSORIL®, Natreon Inc, USA), containing not less than 10% withanolide glycosides, not more than 0.5% of withaferin-A.

Placebo caps contained cellulose, lactose, and magnesium stearate.

Outcome Measures

Assessment was measured through psychomotor performance testing, including the following 6 tests. Each test was administered thrice, then averaged.

  • Finger tapping test (FTT): information on motor system performance
  • Simple reaction test (SRT): attention and sensory-motor performance of brain
  • Choice discrimination test (CDT): attention and sensory-motor performance of the brain and estimation of the psychomotor response speed
  • Digit symbol substitution test (DSST): attention, response speed, central integration, and visuo-motor coordination
  • Digit vigilance task (DVT): alertness and vigilance
  • Card sorting test (CST): sensory, motor, central integrative, and executive functions

Key Findings

This study was specifically carried out to evaluate the effects of Withania somnifera on cognitive and psychomotor performance in healthy human participants. After 14 days of treatment with Withania somnifera, outcomes showed significantly improved reaction time in 5 of the 6 psychomotor performance tests, with no sedative effects, when compared to placebo and to baseline testing. There was no effect on the finger tapping test (FTT), which measures general information on motor system performance.

The mechanism of action in humans is not clear, yet through animal studies, it is linked to the Sitoindosides VII–X and Withaferin A (glycowithanolides) producing an increase in cortical muscarinic acetylcholine capacity, with a modulation of cholinergic neurotransmission. The indication here is that the use of Withania somnifera can bring significant changes in neurological baseline functions, with the postulation that it can be applied clinically in prevention, and possibly repair, of central nervous system disorders.

Practice Implications

In Ayurvedic medicine, Rasayana herbs promote a youthful state of physical and mental health and expand happiness.1 The herbs that are considered Medhya Rasayana are said to be working with the higher brain function, or mind-rejuvenating herbs. They engender and summon intelligence, memory, and mental perception2 and bring nervine and nervous system restorative action. Brahmi (Bacopa monniera), used for improving memory in dementia; and Vacha (Acorus calamus), Sweet Flag, thought to improve blood circulation in the brain, are 2 significant plants in this group. Other herbs included in the Medhya Rasayana group are Mandukparni (Centella asiatica), Gotu kola, described in spiritual practices as opening the crown chakra; Shankhapushpi (Convolvulus pluricaulis), the simple bind weed, thought to improve memory and prevent memory loss; Jyotishmati (Celastrus paniculatus), a native to India, called the intellect tree, thought to stimulate the intellect and sharpes the memory; and Jatamansi (Nardostachys jatamansi), a highly aromatic Valeriana family plant known to have biphasic action on the nervous system, stimulation, and sedation as needed.3,4

Withania somnifera, a Solanaceae family plant, holds the most prominent place of the Ayurvedic Rasayana herbs, acting as an adaptogen, rejuvenating the nervous system, and enhancing the body’s resilience to stress.5

This study's range of testing is narrow, the number of participants is small, and the demographics are limiting. The outcomes, however, point to what has been observed for thousands of years in Ayurvedic Medicine: That Withania somnifera promotes physical and mental health. Traditionally, Ashwagandha is considered the best tonic for old people and for children, and as an aphrodisiac for young people. Through many current studies, as well as clinical observations, it is shown that this humble Rasayana herb works in a diversity of ways toward this goal of promoting physical and mental well being.

Improves Cognitive Function

For focus, concentration, and memory, Ashwagandha has been shown in many studies to enhance all aspects of cognitive function. A double-blind, placebo-controlled clinical study compared the effects of Withania somnifera, Panax ginseng, and placebo on psychomotor performance in 30 healthy participants. Sensorimotor function, auditory reaction time, and mental arithmetic ability were improved in the Withania somnifera arm compared to Panax ginseng and placebo.6

Adaptogenic action, stress management

The glycowithanolides mimic the body’s own stres- reducing relaxation hormones, which reduces cortisol. Overall energy levels can be enhanced through optimizing mitochondrial function. Withania somnifera helps to maintain homeostasis, a sense of presence and focus, throughout times of stress. Ashwagandha is a calming adaptogen—one of the few adaptogens that can be taken later in the day or even at bedtime.


Effectively utilized with people struggling with anxiety, insomnia, nervous exhaustion, and mild OCD, Withania somnifera has GABA-mimicking effects. In one Indian study done on rats, a bioactive glycowithanolides isolate made from the roots of the plant showed results comparable to those elicited by the benzodiazepine lorazepam for anxiety and the tricyclic anti-depressant imipramine for depression.7

Neurodegenerative disorders

Through antioxidant and inflammation-modulating mechanisms, it appears that Withania somnifera can act preventatively, as well as repairing function, for neurodegenerative diseases including Alzheimer's,8 Parkinson's disease,9 and Huntington's disease. All neurodegenerative diseases are accelerated by stress, and as stress increases in the overall population, we are seeing increased numbers of people, and people at earlier ages, showing signs of dementia and early-onset Alzheimer's disease. The adaptogenic action and stress management support from Ashwagandha can slow down the development of these diseases of the brain and nervous system.


Ashwagandha is reported to promote increased production of all stem cells. One study done to evaluate the potential toxicity of Withania somnifera and Panax ginseng when given together not only found that there was no toxicity, but that hematopoiesis was improved.10 I have found this blood cell–building ability of Ashwagandha effective repeatedly in my clinical practice, used when there are low RBCs in iron deficiency anemia, when there are low WBCs in chronic viral disease or as a result of chemotherapy, and when there are low platelets.

Treatment of opiate addiction

Being a nervous system tonic, Withania somnifera can be given to support the severe response to withdrawal from opiate drugs. Ashwagandha can provide protection and regeneration of neurons, and when given prior to heroin withdrawal may ease the withdrawal symptoms. Taken long-term, it can prevent the loss of dopaminergic density in the nucleus procumbens, which usually happens with opiate withdrawal.11,12

With its adaptogenic action on the body in the face of stress and its mind-rejuvenating effects helping to maintain effective cognitive function throughout life, Withania somnifera is an extremely valuable ally in clinical practice.

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  1. Singh N, Bhalla M, De jager P, Gilca M. An overview on ashwagandha: a Rasayana (rejuvenator) of Ayurveda. Afr J Tradit Complement Altern Med. 2011;8(5 Suppl):208-13.
  2. Khalsa KP, Tierra M. The Way of Ayurvedic Herbs, The Most Complete Guide to Natural Healing and Health with Traditional Ayurvedic Herbalism. Lotus Press; 2008.
  3. Ibid.
  4. Caldecott T. Ayurveda, The Divine Science of Life. Elsevier Health Sciences; 2006.
  5. Bhattacharya SK, Goel RK, Kaur R, Ghosal S. Anti-stress activity of sitoindosides VII and VIII, new acylsterylglucosides from Withania somnifera. Phytother. Res. 1987;1(1):32-37.
  6. Karnick CR. A double-blind, placebo-controlled clinical studies on the effects of Withania somnifera and Panax Ginseng extracts on psychomotor performance in healthy Indian volunteers. Indian Med. 1991;3:1–5.
  7. Bhattacharya SK, Bhattacharya A, Sairam K, Ghosal S. Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental study. Phytomedicine. 2000;7(6):463-469.
  8. Bhattacharya SK, Kumar A, Ghosal S. Effects of glycowithanolides fromWithania somnifera on an animal model of Alzheimer's disease and perturbed central cholinergic markers of cognition in rats. Phytother. Res. 1995;9(2):110-113.
  9. Nagashayana N, Sankarankutty P, Nampoothiri MR, Mohan PK, Mohanakumar KP. Association of L-DOPA with recovery following Ayurveda medication in Parkinson's disease. J Neurol Sci. 2000;176(2):124-127.
  10. Aphale AA, Chhibba AD, Kumbhakarna NR, Mateenuddin M, Dahat SH. Subacute toxicity study of the combination of ginseng (Panax ginseng) and ashwagandha (Withania somnifera) in rats: a safety assessment. Indian J Physiol Pharmacol. 1998;42(2):299-302.
  11. Ruiu S, Longoni R, Spina L, et al. Withania somnifera prevents acquisition and expression of morphine-elicited conditioned place preference. Behav Pharmacol. 2013;24(2):133-143.
  12. Kasture S, Vinci S, Ibba F, et al. Withania somnifera prevents morphine withdrawal-induced decrease in spine density in nucleus accumbens shell of rats: a confocal laser scanning microscopy study. Neurotox Res. 2009;16(4):343-355.