I'm not an expert, but have looked into using Evolve and Contrapest. My understanding is that their active ingredient is gossypol, derived from unrefined cottonseed oil. I have used both the oil (ineffective) and lab-made gossypol extract on my garden rats at daily doses of 10-20mg. I haven't been able to gauge the effectiveness in reducing litter sizes because these vary by season anyway, but on camera, I haven't seen any pregnant-looking females in several weeks.
I'm not an expert, but have looked into using Evolve and Contrapest. My understanding is that their active ingredient is gossypol, derived from unrefined cottonseed oil. I have used both the oil (ineffective) and lab-made gossypol extract on my garden rats at daily doses of 10-20mg. I haven't been able to gauge the effectiveness in reducing litter sizes because these vary by season anyway, but on camera, I haven't seen any pregnant-looking females in several weeks.