AUGUST 2021 - DUE TO COVID-19 LIMITING SPAY/NEUTER SURGERIES, ALLEY CAT ALLIES AND THE ALLIANCE FOR CONTRACEPTION IN CATS AND DOGS NOW ENDORSE THE SHORT TERM USE OF MA TO PREVENT PREGNANCIES IN CATS- SEE THEIR WEBSITES FOR MORE INFORMATION 

Edible Birth Control for Cats

It works, is low risk, *LOW COST, 
and can save millions of cats' lives. 

This blog is my opinion based on years of personal experience and dozens of hours of research. I am not a veterinarian. I am an animal lover who has particular empathy for feral cats who are outside through no fault of their own and historically have been euthanized by animal control. . 

Megestrol Acetate is a synthetic progesterone/hormone available by prescription only in the United States. It has been found to be effective as a birth control in cats ( see below) Do thorough research and give careful consideration before making your own decision about obtaining or using Megestrol Acetate.

It works -

I have used both Feralstat and Nonovulin with success for over 15 years. A colleague writes about his positive experience on Birthcontrolforcats.com. Fairchild Feral Friends has used it for over a decade to stabilize colonies while T/N/R is being done. A Topix forum (please see archived posts) has caretakers from all over the country discussing their success. And it has been available without a prescription in pharmacies in Europe for more than 20 years. In June of 2025 I purchased two packages of 30 ten mg tablets from petshopboss.com for $36.00.   

It's low risk -

The following French study took place after a consumer voiced concerns about side effects of megestrol acetate products for cat birth control. Even though the manufacturer's recommended dosage is much higher than the dose U.S. feral cat caretakers use, risk of side effects was determined to be .074 per 100K pills sold. An English translation as well as the original French study is available through the birthcontrolforcats.com website at  http://www.birthcontrolforcats.com/cnpv.pdf

My own research (see archive) found very little research in the U.S., and all at much higher doses. A European study was more extensive and showed very low risk of adverse reaction. 

Along with two feral colonies, I have used Nonovulin successfully on two indoor cats for which surgery was high risk, with no negative side effects.   

It's low cost

*In June of 2025 I paid $36 for two 30 ten mg Nonovulin pills through petshopboss.com. Although I encountered what appeared to be a security issue early in the ordering process, they replied quickly and with documentation which assured me that the site was safe. I received the product in a timely manner and my payment was processed without issue. Prior to that I had ordered Nonovulin through eBay.

 

Nonovulin is a megestrol acetate product available in pharmacies in Europe. In the U.S. megestrol acetate is prescription only.. 

                                                               My Second Colony

When I began feeding and dosing in September of 2019 there were 17 cats. There were no births. New adult cats joined the group. Three young cats and one ill adult came home with me. By 2023 the colony was gone.   

I've used the chart below from Fairchild Feral Friends to determine dosage. I cut the 10 mg pills with a pill cutter and dissolve the dosage in a little water in a clear container so that I can see that the particles are well dissolved before adding them to one 22 oz can of wet cat food. 

Please note that the dosage is PER COLONY NOT PER CAT.   

Dosage PER COLONY  using Nonovulin 10 mg tablets

                                                Total # of Cats           Dosage (dry) per colony 
  

                                                       < 5 cats                       2.5 mg once a week

                                                          5-7 cats                    5 mg once a week

                                                          8-11 cats                  7.5 mg once a week

                                                          12-15 cats                5 mg twice a week

                                                          16-19 cats                7.5 mg twice a week

                                                          20-23 cats                8 mg twice a week

                                                          24-27 cats                10 mg twice a week 

                                                          28-31 cats                11 mg twice a week

                                                          32-35 cats                12.5 mg twice a week c      

          2.8 ml  TWICE A WEEK                        14 mg TWICE A WEEK

This information was previously published on my site floridacatnews.com.