My only dealings with ATOS have been related to qualification for benefits not medication.
Most GP Surgeries run their own budgets (though not all) so obviously they do want to be sure they are only prescribing the medication the patient is using.
Certain prescriptions require more thorough reviewing as long term use can have other side effects after a while, blood tests etc to test that they are not causing problems elsewhere in the body.
I'm sure your review will be fine, just be calm and explain how things are with you and what helps you.