Azathioprine has been found to cause ultra UV ray sensitivity by UK researchers. They also found a higher incidence of skin cancers in those taking Azathioprine. This study was done on patients taking much higher doses but it does serve as a cautionary warning for those of us that use or have used Azathioprine.
Also other medications can cause sun sensitivity. My GP changed my blood pressure medicine some years back [pre-Internet]. He failed to mention that my new med would make one extra sensitive to the sun. Was out doors without sun screen and got a burn on my chest and neck that I still have 20 years later......
http://news.bbc.co.uk/2/hi/health/4248356.stm