Ashwagandha is an herb that has been widely used in Ayurveda, an ancient Indian medicine based on natural remedies, for over 3000 years. Having a botanical name, Withania Somnifera, Ashwagandha is also known as Indian ginseng or winter cherry. It grows in Africa, the Mediterranean, and India and grows to 30-150cm in height.  The whitish brown root of Ashwagandha is the main therapeutic ingredient, historically used for anti-inflammatory effect, rejuvenation, disease prevention, and treatment for various infections.  Currently, much research has scientifically shown the promising effects of Ashwagandha.
Anti-stress, anti-anxiety, anti-depression
Several pre-clinical and clinical studies have shown that Ashwagandha has strong anxiolytic effects potential. In a pre-clinical study with rats, extracts from Ashwagandha roots were orally administered to the rats for 5 days and compared with current anxiolytic and antidepressant drugs (lorazepam, imipramine). Ashwagandha extract showed comparable anxiolytic and antidepressant effects as lorazepam and imipramine.
A double-blind placebo-controlled clinical study was done on 39 subjects with anxiety disorders. After 6 weeks of orally administering 250mg tablet of ethanolic Ashwagandha extract twice a day, 88.2% of the patients’ anxiety score was decreased to ‘no anxiety’ criteria which is significantly better than the placebo group (50%). Another study was done on patients with chronic stress. 64 Patients received 300 mg of Ashwagandha root extract twice a day for 60 days. The Ashwagandha root extract was able to induce a significant reduction in the stress-assessment score and serum cortisol level. 
A larger-scale investigation would be more beneficial, but the current studies support Ashwagandha's promising effect on anxiety, stress, and depression.
The thyroid is a small organ located in the front of the neck which has a very important function in body homeostasis. It produces hormones to control body temperatures and heart rate as well as how much energy to use. Hypothyroidism, lack of thyroid activity, can cause mild symptoms like fatigue, weight gain, depression, loss of sexual interest to severe symptoms such as heart failure and coma.
Triiodothyronine (T3) and Thyroxine (T4) are the two most important hormones which are downregulated in hypothyroid patients. In a pre-clinical rat model of hypothyroidism, hypothyroidism rats treated with Ashwagandha extract showed significant improvement in both serum T3 and T4 levels compared to the placebo. Although the extract was not as effective as hypothyroidism medicine (Eltroxin), the result was comparable. However, even in normal rats without hypothyroidism, the extract increased both T3 and T4 levels. [6,7]
A few clinical studies on hypothyroidism are available as well. In a study to treat bipolar disorder patients with Ashwagandha extracts, scientists noticed subtle increases in T4 levels. In another clinical study with subclinical hypothyroidism patients, a patient group which administered 600mg of the root extract for 8 weeks showed significant improvement in serum T3 and T4 level. 
Current scientific evidence shows that Ashwagandha extract is effective in increasing thyroid hormones level. However, caution is required since it can increase thyroid hormone levels even in healthy and hyperthyroidism individuals.
Cognitive decline comes along with aging. Ashwagandha has been used to reverse the memory and cognitive decline for a long time in Ayurveda and it is currently scientifically investigated on its efficacy for improving cognitive ability. In a review of 5 currently available clinical studies, all of the 5 studies showed significant improvement in cognitive functions such as reaction time, memory, and information processing speed, compared to the placebo groups. The study subjects were diverse including healthy young males age 20-35, bipolar patients, and children with mental retardation. 
Ashwagandha extract has various alkaloids including Withaferin A (WFA) which is proven to be toxic to various cancer cells. Many in vitro studies with cancer cell lines propose numerous mechanisms such as enhancing reactive oxygen species production, NF-𝜅B inhibition, increase inflammatory cytokine, cell cycle arrest, and apoptosis in which ashwagandha can treat cancers. Active ingredients, especially WFA have shown apoptotic efficacy in breast, prostate, pancreatic, colorectal, leukemic, and ovarian cancer cells. Moreover, the ashwagandha extract can potentiate current radio- and chemotherapy through radio- and chemosensitization. 
In Addition to potential cancer therapeutic efficacy, Ashwagandha can alleviate some symptoms in patients going through chemotherapy. In phase II clinical study of combined ashwagandha extract and chemotherapy in breast cancer, patients with combined therapy felt much less fatigue, had a significantly better quality of life, and longer survival of the patients compared to chemotherapy alone. 
Currently, there are no clinical trials on human subjects to test its efficacy in treating cancer cells. However, considering abundant clinical evidence on the safety of ashwagandha for oral administration, orally administering it less than 1000 mg/day might be worth a try.
Ashwagandha has shown no major side effects in both pre-clinical and clinical studies when administered orally (up to 2000mg/kg per day). In the rat models, Ashwagandha was proved to be safe even for the fetus and pregnant mothers. However, direct intraperitoneal (abdomen) injection has shown acute toxicity and therefore, injection of Ashwagandha extract is strongly discouraged. Based on current animal models and small-scale clinical studies, it can be considered a safe medicinal herb for natural remedies against various diseases.[5,12]
- Gupta, G.L., & Rana, A.C. (2019). PHCOG MAG.: Plant Review Withania somnifera (Ashwagandha): A Review.
- Mishra, L. C., Singh, B. B., & Dagenais, S. (2000). Scientific basis for the therapeutic use of Withania somnifera (ashwagandha): a review. Alternative medicine review : a journal of clinical therapeutic, 5(4), 334–346.
- Bhattacharya, S. K., Bhattacharya, A., Sairam, K., & Ghosal, S. (2000). Anxiolytic-antidepressant activity of Withania somnifera glycowithanolides: an experimental study. Phytomedicine : international journal of phytotherapy and phytopharmacology, 7(6), 463–469. https://doi.org/10.1016/S0944-7113(00)80030-6
- Andrade, C., Aswath, A., Chaturvedi, S. K., Srinivasa, M., & Raguram, R. (2000). A double-blind, placebo-controlled evaluation of the anxiolytic efficacy ff an ethanolic extract of withania somnifera. Indian journal of psychiatry, 42(3), 295–301.
- Chandrasekhar, K., Kapoor, J., & Anishetty, S. (2012). A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian journal of psychological medicine, 34(3), 255–262. https://doi.org/10.4103/0253-7176.106022
- Hosny, E. N., El-Gizawy, M. M., Sawie, H. G., Abdel-Wahhab, K. G., & Khadrawy, Y. A. (2020). Neuroprotective Effect of Ashwagandha Extract against the Neurochemical Changes Induced in Rat Model of Hypothyroidism. Journal of dietary supplements, 1–20. Advance online publication. https://doi.org/10.1080/19390211.2020.1713959
- Abdel-Wahhab, K. G., Mourad, H. H., Mannaa, F. A., Morsy, F. A., Hassan, L. K., & Taher, R. F. (2019). Role of ashwagandha methanolic extract in the regulation of thyroid profile in hypothyroidism modeled rats. Molecular biology reports, 46(4), 3637–3649. https://doi.org/10.1007/s11033-019-04721-x
- Sharma, A. K., Basu, I., & Singh, S. (2018). Efficacy and Safety of Ashwagandha Root Extract in Subclinical Hypothyroid Patients: A Double-Blind, Randomized Placebo-Controlled Trial. Journal of alternative and complementary medicine (New York, N.Y.), 24(3), 243–248. https://doi.org/10.1089/acm.2017.0183
- Ng, Q. X., Loke, W., Foo, N. X., Tan, W. J., Chan, H. W., Lim, D. Y., & Yeo, W. S. (2020). A systematic review of the clinical use of Withania somnifera (Ashwagandha) to ameliorate cognitive dysfunction. Phytotherapy research : PTR, 34(3), 583–590. https://doi.org/10.1002/ptr.6552
- Dutta, R., Khalil, R., Green, R., Mohapatra, S. S., & Mohapatra, S. (2019). Withania Somnifera (Ashwagandha) and Withaferin A: Potential in Integrative Oncology. International journal of molecular sciences, 20(21), 5310. https://doi.org/10.3390/ijms20215310
- Biswal, B. M., Sulaiman, S. A., Ismail, H. C., Zakaria, H., & Musa, K. I. (2013). Effect of Withania somnifera (Ashwagandha) on the development of chemotherapy-induced fatigue and quality of life in breast cancer patients. Integrative cancer therapies, 12(4), 312–322. https://doi.org/10.1177/1534735412464551
- Mandlik Ingawale, D. S., & Namdeo, A. G. (2020). Pharmacological evaluation of Ashwagandha highlighting its healthcare claims, safety, and toxicity aspects. Journal of dietary supplements, 1–44. Advance online publication. https://doi.org/10.1080/19390211.2020.1741484