Hello, I'd like to help you with your question.
Xanax and Valium are both benzodiazepines and are prescribed mainly to help with anxiety. Both can be addicting. It is recommended that they be used short term only although longer term use is ok under a doctor's supervision.
In studies, the effectiveness of Xanax is limited to 4 months for anxiety disorder and up to 10 weeks but as long as 8 months without loss of benefit from the drug.
For Valium, use up to 4 months has been evaluated. After that, the doctor should re evaluate the person for effectiveness.
Each person is different in how they react to medications because of factors like height, weight and health concerns. Also, metabolism must be factored in. Some people have fast metabolisms and therefore process medications differently than someone with a slower system.
I hope this has helped you,