In A Woman's Book of Choices: Abortion, Menstrual Extraction, RU-486
by Rebecca Chalker and Carol Downer,
vitamin C is described as working best as an abortifacient when taken right at the time that very first missed period is due. There was a study in the seventies in Russia in which 20 pregnant women took about six grams of ascorbic acid for three days, and all but four had started to menstruate by the end of the three days.
The study has not been duplicated since (to these authors' knowledge, or mine) but if it works, the earlier on, the more effective. Even a few days after that missed period can make the difference.
In Susun Weed's Herbal for the Childbearing Year, she writes:
"Ascorbic acid is the safest and reportedly most effective emmenagogue that can be used after the menstrual flow has failed to appear. Women report success even when three weeks 'late.' Six grams of vitamin C is the daily dosage needed to abort. Take 500 mg ever hour for 12 hours a day for up to six days."
I'll leave it to an expert to really answer the question, but that's what I've got.

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