Actually you should not take any medicine without doctors advice. It will be more helpful if you let know for what problem you are taking Ashwagandha. It is ' balya' medicine which is useful in generalized weakness, Has Aphrodisiac properties. Also useful in Anxiety and stress, various 'Vaat roga' such as osteoarthritis, parkinsonism, etc. Dose is variable according to the condition in which it has to be used. General dose of powder is 500mg twice daily with milk.
Take an expert advise so that doctor can help you out from the condition along with the combinations of some other medicines also, if required.