6MP is a safe drug. Back when I took it in the late 1990s there were some concerns about it's long term side effects but in the early 2000s they deemed this drug safe. UCers take a lower dose than cancer patients. Honestly, I never had any side effects from taking the drug and now 8 years after my last dose I have noticed no long term side effects.
dx proctitis in 1987
dx UC in 1991, was stable until 1998
1998 started prednisone, asacol, pentasa, nortriptylene, ativan, 6MP, rowasa enemas and suppositories, hydrocortisone enemas, tried the SCD diet, being a vegetarian, omega 3s, flax, pranic healing, yoga, acupuncture, probiotics
2000 lost all my B-12 stores and became anemic
2001 opted for j-pouch surgery- now living life med-free