I. People can be extremely sensitive or even badly allergic to individual medications. The side effects that one might show is highly variable.
But when someone tries to palm off that they are generally "sensitive to medications" in a psychiatric context, they really mean they don't want to be given medication. All porridge will be either too hot or too cold. No porridge will be just right.
II. To a patient challenging your credentials, no credentials will be good enough. You can be "International Psychiatrist of the Year" six years running, with additional degrees in brain science, multicultural psychology, and spelling reform, but it won't be quite right.