I just gave my cat a 1/4 teaspoon of Miralax.. She is back and forth to litter box but no results for her. How Long does it Take Miralax to start working? Its been about 20 minutes since I gave her first dose. She spent the weekend at vet cause she was so blocked she pushed her rectum out of place.. So they put her under and cleaned her out and she has been home two days and hasn't used litter box. She started going to litter box last night and been trying to pass a bowel but nothing yet .. Saw this site and read about the Miralax so giving it a go .. Any advice is greatly appreciated .. I do not have the funds to keep bringing her to vet so praying this works.. She has a litter of newborn kittens also .. I didn't think about it till now but will this get them sick through her milk with her having taken Miralax?