CANCER doctors are on a collision course with a Catholic health organisation over new religion-based rules which prohibit them recommending contraception to patients taking a drug derived from thalidomide, which can cause severe birth defects.

Under a clampdown at Newcastle's Calvary Mater Hospital, doctors recruiting patients into clinical trials may no longer distribute information about contraception. Instead they are allowed to offer a ''statement of reproductive risks'', which advises participants to avoid pregnancy but gives no information on how to achieve this.

"It puts me in an invidious position" ... Dr Michael Seldon, a practising Catholic who works at Newcastle's Calvary Mater Hospital. Credit:Anita Jones

Michael Seldon, a staff specialist haematologist at the hospital, which operates as part of NSW Health and is the city's only cancer treatment centre, said he was considering defying his bosses and providing the information anyway when the first Newcastle patients suffering myelodysplastic syndrome, multiple myeloma or chronic lymphocytic leukaemia join national trials of the drug lenalidomide within weeks.

The drug's chemical structure is extremely similar to thalidomide, and the risk of birth defects such as limb and heart deformities is considered so serious that its manufacturer, Celgene, advises even men who have had a vasectomy to use a condom. It insists women have two negative pregnancy tests before starting treatment, and then use two forms of contraception simultaneously.