You'll get some information here:
http://www.jaa.nl/licensing/manual_2...%20MedaFly.pdf
I'm pretty sure that under JAR rules methotrexate (a cytotoxic) and oral corticosteroids are disqualifying.
Not completely sure about the others, but a phone call to one of the Aeromedical Advisors at the CAA would almost certainly provide more answers.
If your arthritis is bad enough to need all those items, would you really be physically able or comfortable to carry out the pilot's task ? (Bearing in mind that that includes all the pre-flight walk-around, and a requirement to be able to exit quickly in emergency. Being a pilot involves more than just sitting at a control column, and staring at the instruments).