OBJECTIVE: The objective of this paper is to review the literature regarding Withania somnifera (ashwagandha, WS) a commonly used herb in Ayurvedic medicine. Specifically, the literature was reviewed for articles pertaining to chemical properties, therapeutic benefits, and toxicity.
DESIGN: This review is in a narrative format and consists of all publications relevant to ashwagandha that were identified by the authors through a systematic search of major computerized medical databases; no statistical pooling of results or evaluation of the quality of the studies was performed due to the widely different methods employed by each study.
RESULTS: Studies indicate ashwagandha possesses anti-inflammatory, antitumor, antistress, antioxidant, immunomodulatory, hemopoietic, and rejuvenating properties. It also appears to exert a positive influence on the endocrine, cardiopulmonary, and central nervous systems.
The mechanisms of action for these properties are not fully understood.
Toxicity studies reveal that ashwagandha appears to be a safe compound.
CONCLUSION: Preliminary studies have found various constituents of ashwagandha exhibit a variety of therapeutic effects with little or no associated toxicity. These results are very encouraging and indicate this herb should be studied more extensively to confirm these results and reveal other potential therapeutic effects. Clinical trials using ashwagandha for a variety of conditions should also be conducted. (source)
Here is a study that specifically shows Ashwagandha as being effective in reducing the pain of arthritis.
Treatment of osteoarthritis with a herbomineral formulation: a double-blind, placebo-controlled, cross-over study.
Kulkarni RR, Patki PS, Jog VP, Gandage SG, Patwardhan B.
Bryamjee Jeejeebhoy Medical College, University of Poona, Pune, India.
The clinical efficacy of a herbomineral formulation containing roots of Withania somnifera, the stem of Boswellia serrata, rhizomes of Curcuma longa and a zinc complex (Articulin-F), was evaluated in a randomized, double-blind, placebo controlled, cross-over study in patients with osteoarthritis.
After a one-month single blind run-in period, 42 patients with osteoarthritis were randomly allocated to receive either a drug treatment or a matching placebo for a period of three months.
After a 15-day wash-out period the patients were transferred to the other treatment for a further period of three months.
Clinical efficacy was evaluated every fortnight on the basis of severity of pain, morning stiffness, Ritchie articular index, joint score, disability score and grip strength.
Other parameters like erythrocyte sedimentation rate and radiological examination were carried out on a monthly basis.
Treatment with the herbomineral formulation produced a significant drop in severity of pain (P less than 0.001) and disability score (P less than 0.05). Radiological assessment, however, did not show any significant changes in both the groups. Side effects observed with this formulation did not necessitate withdrawal of treatment. (source)
The two studies quoted above are shown, in abstract form, on this web site. In addition to such references within the 40 pages on just one of the herbs in this product are more references, such as:
Withaferin Aexhibits fairly potent anti-arthritic and anti-inflammatory activities. It was found to suppress arthritic syndrome without any toxic effect. Unlike hydrocortisone-treated animals which lost weight, the animals treated with withaferin A showed gain in weight in arthritic syndrome. It is interesting that withaferin A seems to be more potent than hydrocortisone in adjuvant-induced arthritis in rats, a close experimental approximation to human rheumatoid arthritis. In its oedema-inhibiting activity, the compound gave a good dose-response in the dose-range of 12-25 mg./kg. body-wt. of albino rats intraperitoneally and a single dose had a good duration of action, as it could effectively suppress the inflammation after four hours of its administration. The effect of the withanoloide in suppressing granulation-tissue formation appeared to be similar to that of hydrocortisone. The locally induced graft (lymphocytes)-versus-host reaction in chicks was strongly inhibited by withaferin A (Sethi et al., Indian J Pharmacol.,1970, 2, 165; Chem. Abstr.,1973, 79, 142880) (source)
Studies like these are usually written in very technical language, but you can get the idea here that a considerable amount of scientific study has been done with this and other herbs. Since the Indian tradition of Ayurveda has existed for more than 5,000 years, there is not only the history of usage of various herbs for specific situations, but a long-standing opportunity to do a scientific study of the ancient claims. It is startling to find that this ancient wisdom, going back 5,000 years, is so fully validated by modern scientific methods.
DESIGN: This review is in a narrative format and consists of all publications relevant to ashwagandha that were identified by the authors through a systematic search of major computerized medical databases; no statistical pooling of results or evaluation of the quality of the studies was performed due to the widely different methods employed by each study. 
Withaferin Aexhibits fairly potent anti-arthritic and anti-inflammatory activities. It