McALLEN, Texas — 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.

And knowledge of what the correct dosage is seems to be in short supply among the pharmacy workers dispensing the drugs in northern Mexico. Researchers say that the brand-name form of the medication, Cytotec, made by Pfizer, has been available over the counter in Mexico since 1985 and that generic versions have followed. The drug is available in many small, independent pharmacies in the country, but the people selling it often lack training. Because abortion is illegal outside the country's capital city, they are also wary of providing information on how misoprostol should be used for that purpose.

Without proper instructions, Banda said, her clinic's patients have often ingested misoprostol in varying amounts — some would take an entire bottle within days — based on what friends or family had told them.

Dan Grossman, an obstetrician-gynecologist who is vice president for research at Ibis Reproductive Health and an assistant professor at the University of California, San Francisco, stressed that misoprostol was a safe drug when used properly, for example to prevent bleeding during labor and to control uterine contractions.

"The biggest risk for these women is that it's not going to be effective" at ending their pregnancies, he said. A woman for whom the drug doesn't work might well not know it, he added. "She could potentially have a continuing pregnancy and not get a follow-up."

Indeed, many health providers also say that women crossing into Mexico to buy misoprostol are ignoring important follow-up care.

Abortion-rights advocates are concerned that a lack of awareness about clinical options in the United States — as well as a lack of funds — could lead more women to go underground and risk their health in this way. In 2011, Texas lawmakers made deep cuts in financing for family planning for low-income women. And a new law that requires a woman seeking an abortion to receive a sonogram 24 hours ahead of the procedure — that is, to make at least two visits to the abortion clinic — may be prompting some to seek alternate abortion methods.

Women Banda talked to who sought out misoprostol in Mexico, she said, were looking for "the least invasive option, both medically and personally."

She added that it was likely that her clinic was seeing only a fraction of the women who were using the drug. South Texas has a concentration of immigrants who were born in Latin American countries, where self-medication is a common practice and abortion is outlawed or culturally stigmatized.

Mexico City legalized abortion in 2007, but the historical lack of access throughout the country has contributed to the popularity of misoprostol for its unlabeled use, especially in poor areas where pharmacy regulations are largely unenforced, according to a 2010 study in International Perspectives on Sexual and Reproductive Health.

In July, at one of the many pharmacies lining the main street in Nuevo Progreso, a town across the border from Weslaco, Jose Alfredo Acosta was selling Cytotec for $153 per box. The package contained 28 pills, each about 200 micrograms. The informational insert did not include directions for self-induced abortion, but Acosta said he knew that was why many women bought the medication.

"If I see that a girl is too young, I won't sell it," he said, citing stories he had heard of girls hemorrhaging after using the pills. "I try my best to explain the consequences, but there's only so much I can do."

Like many Progreso pharmacy workers, Acosta does not hold a pharmacy degree or a license but is allowed under Mexican law to dispense Cytotec. Asked about the proper dosage, he reluctantly suggested that patients take one pill every two hours — 18 tablets in all.

According to the World Health Organization, the recommended dosage of misoprostol, if used alone for an abortion, should be four tablets (800 micrograms) every three hours for a total of three doses, or 12 tablets.

Gabriel Noguez, who works in a pharmacy down the street from Acosta and is also untrained, said his shop sold Cytotec for $241.80 per box.

"It sells. That's the problem," he said. "But I won't tell them how to take it. I just say, 'You might have problems later.' "

Grossman said he was concerned that the misoprostol issue was a symptom of the barriers women faced in getting a legal abortion in the United States, especially for those who were determined to end their pregnancies.

In a 2010 study he published in the journal Reproductive Health Matters, a 30-year-old Texas woman reported that she started taking misoprostol in her 13th week of pregnancy. She bled so badly that she had to be admitted to a hospital.

The woman said cost was the factor behind her decision to try misoprostol instead of visiting a clinic. But she had no regrets.

"If I was put in the exact situation all over again," she was quoted as saying, "I'd probably do it again."

This story was made possible by a grant from Atlantic Philanthropies, and was produced as part of New America Media's Women Immigrants Fellowship Program. It was also published in The New York Times.