After my Herceptin treatments started showing less effectiveness, my Dr. Prescribed Tykerb along with Herceptin. I take 4 pills daily and have been for 3 months. Side effects for me a tolerable...some diarreha but Imodium works to stop it. Also take Phillips Colon Health Probiotic. That is what helped me the most with Diarreha while going through chemo. Dr is monitoring me every 3 weeks. So far...so good.