MCALLEN — In this Roman Catholic stronghold, where abortion is deeply stigmatized, reproductive health providers tell stories of women going to pharmacies across the border in Mexico, in search of a drug they hope will terminate unwanted pregnancies.

But the providers say that the pharmacies, which are largely unregulated, often fail to give proper instructions for the drug, misoprostol, and that it does not always give the women the result they seek.

“I’m sure it’s always occurred, but we’re noticing it more,” said Kristeena Banda, the director of Whole Woman’s Health in McAllen, one of two Rio Grande Valley abortion providers. “A few times a week, women come in to ask for a pregnancy test. They’ve taken the pills, but they’re still seeing symptoms of pregnancy.”

Misoprostol, which requires a prescription in the United States, is used primarily for ulcer prevention here and is not prescribed, on its own, for abortions. American doctors and clinics do sometimes pair it with the drug mifepristone (formerly known as RU-486) to produce a “medical abortion,” a method considered more effective than using misoprostol by itself. But the World Health Organization has said that using misoprostol alone can be highly effective as an abortion method, provided patients take the correct dosage within the first nine weeks of gestation.