Ashwagandha is generally safe, though extensive studies are not available for longer periods. But if you are on any medication or on any treatment for any other disorder, pls consult your ayurvedic physician or the healthcare professional with whom you consult for other conditions before taking Ashwagandha.
Pregnant & nursing mothers, people on immunosuppressants, those on thyroid medication and those with type 1 diabetes etc, should strictly take advise of their clinicians before use.