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The morning after pill is not known to be effective in dogs. There are numerous methods and/or medications that your vet may be able to offer you. Many will use hormones as a way to terminate pregnancy but this doesn't come without risks. Estrogens may cause bone marrow suppression and increases the risk of a uterine infection. Here is a site that contains loads of information and different methods. Your biggest problem is locating a vet who will dispense medication or treatment to you as many decline to treat when the risk is high for illness and dogs only have a 40% chance of becoming pregnant with just one breeding.
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