The reason for the reduction in effect of medicine can be many , like the progression of disorder , taking medicines irregularly, interaction with other medicines , other medical illness , use of substance that reduces efficiency of medicines etc....
Whether any medicine will be required life long depends upon the underlying disorder and response that the patient shows to treatment.
And the medicine that you will be getting in india will have the same composition but the brand name might differ. Don't worry about medicine quality,here in India you will get branded as well as good generic medicine. As you might be knowing India is the leading manufacturer and supplier of medicines to the world.
Next Steps
Consult a second opinion from Indian Psychiatry.