It is impossible to know how many women in New York or nationwide try to end their pregnancies themselves, but in the vibrant, socially conservative Dominican neighborhoods of Upper Manhattan, the various methods are passed like ancient cultural secrets. In a study of 610 women at three New York clinics in largely Dominican neighborhoods conducted eight years ago, 5 percent said they had taken misoprostol themselves, and 37 percent said they knew it was an abortion-inducing drug. Doctors and community leaders say they have not seen any signs of the phenomenon disappearing, which they find worrisome because of concerns about the drug’s effectiveness and potential side effects.

Sold under the brand name Cytotec, misoprostol is approved to induce abortion when taken with mifepristone, or RU-486; doctors also sometimes use it to induce labor, though it is not approved for that use. A spokesman for Pfizer, which manufacturers Cytotec, declined to comment beyond saying that the company does not support the off-label use of its products and noting that the label includes “F.D.A.’s strongest warning against use in women who are pregnant.”

That warning, in capital letters, also notes that the drug “can cause abortion.”

But it does not always do so, not least because notions of how best to use it vary from inserting several pills into the vagina to letting them dissolve under the tongue. The side effects can be serious, and include rupture of the uterus, severe bleeding and shock.

“We do worry because we don’t know where women are getting the instructions from,” said Jessica Gonzalez-Rojas of the National Latina Institute for Reproductive Health, which was also a partner on the Ibis study. “We imagine that there is misinformation on how to take it, which is why it could be hit or miss.”

In 2007 in Massachusetts, an 18-year-old Dominican immigrant named Amber Abreu took misoprostol in her 25th week of pregnancy and gave birth to a 1-pound baby girl who died four days later; a judge sentenced her in June to probation and ordered her into therapy. In South Carolina in February, a Mexican migrant farm worker, Gabriela Flores, pleaded guilty to illegally performing an abortion and was sentenced to 90 days in jail for taking misoprostol while four months pregnant in 2004. A Virginia man, Daniel Riase, is serving a five-year prison sentence after pleading guilty in 2007 to slipping the pills into his pregnant girlfriend’s glass of milk.

Researchers studying the phenomenon cite several factors that lead Dominican and other immigrant women to experiment with abortifacients: mistrust of the health-care system, fear of surgery, worry about deportation, concern about clinic protesters, cost and shame.

“It turns an abortion into a natural process and makes it look like a miscarriage,” said Dr. Mark Rosing, an obstetrician at St. Barnabas Hospital in the Bronx who led the 2000 study, which was published in the Journal of the American Medical Women’s Association. “For people who don’t have access to abortion for social reasons, financial reasons or immigration reasons, it doesn’t seem like this horrible thing.”