The text message Cynthia Menchaca received this summer was one she was seeing more and more: A woman living in Texas said she had left a violent relationship only to discover she was pregnant, and she desperately wanted an abortion. The woman had learned that Ms. Menchaca could send her abortion pills from Mexico, where the procedure has been decriminalized in several states.

But the growing U.S. demand for abortion care is not limited to deliveries of medication, according to advocates like Ms. Menchaca, who lives in Coahuila state in northeastern Mexico.

Clinics in Tijuana and Mexico City, as well as activists in the northwestern city of Hermosillo, say they have seen women crossing the border from Texas, Louisiana and Arizona seeking access to abortion.

“Before, the women from Sonora would go to the United States to access abortions in clinics,” said Andrea Sanchez, an abortion-rights activist, referring to the Mexican state that borders Arizona. “And now the women from the United States come to Mexico.”

More than a year after the U.S. Supreme Court overturned Roe v. Wade, Mexican abortion-rights activists have seen a rise of American women crossing the border to seek abortions — crystallizing the shifting policies of two nations that once held vastly different positions on the procedure.

For decades, abortion was criminalized in Mexico and much of Latin America with few exceptions, while in the United States, the 1973 Roe v. Wade ruling established a constitutional right to abortion.

Today, Mexico’s Supreme Court has decriminalized abortion nationwide, making it legally accessible in federal institutions and eliminating federal penalties for the procedure. Twelve of the country’s 32 states have also decriminalized abortion, and activists say they have renewed momentum to push local officials in the remaining states.

By comparison, more than 20 American states currently ban or restrict the procedure after 18 weeks of pregnancy or earlier, with 14 states completely forbidding the procedure in almost all circumstances.

Mexican activists, anticipating the Supreme Court could overturn Roe when it was still weighing the case, began organizing and have established an underground system, sending thousands of pills north and helping women travel south across the border. They say the longstanding restrictions in Latin America prepared them to now handle the influx of demand.

“The truth is that years ago, we neither had nor envisioned collaboration with the United States,” said Verónica Cruz, who 20 years ago helped found the reproductive-rights organization Las Libres, which means “the free ones.”

She added: “But faced with the urgency, the increasing restrictions, and having a model, resources like the pills, and as our territory progresses, it became evident that we needed to build international solidarity.”

Ms. Cruz initially planned to help shuttle women in the United States to Mexico, but found it to be too financially burdensome both for her organization and those seeking abortions. She has instead focused on sending mifepristone and misoprostol, the two-drug regimen to end a pregnancy, over the border to American women, particularly those living in states that ban the procedure or ban providers from prescribing the pills.

In U.S. studies, the combination of these pills causes a complete abortion in more than 99 percent of patients, and is as safe as the traditional abortion procedure administered by a doctor in a clinic. Growing evidence from overseas suggests that abortion pills are safe even among women who do not have a doctor to advise them.

Since the lifting of Roe, Ms. Cruz said she has helped roughly 20,000 women in 23 states secure the abortion pills. She said she will continue to help these women even as certain states move to penalize those who assist with abortions.

Activists involved in sending the pills to the United States declined to specify their shipping and delivery methods, though most said they are coordinating with American activists over the border. One organizer in Mexico, who requested anonymity out of fear of retaliation, said she conceals the medication in electronic accessories, clothing, stuffed animals or dietary supplements when shipping to states that restrict it.

While the Food and Drug Administration said that abortion drugs can be delivered by mail, several states banned this shipping method, or require that the drugs be dispensed by providers in person.

Carol Tobias, the president of the National Right to Life Committee, one of the largest anti-abortion groups in the United States, said she was not surprised that women were traveling to Mexico for abortions. Americans have long crossed the border for various procedures, she said.

But she called for tougher enforcement in the United States to prevent people from easily delivering abortion pills in the mail. “I think it’s very sad that women are being told the abortion pill is an easy, safe way out of a difficult situation,” Ms. Tobias said. “It’s much more complicated than that.”

There is no reliable national data on abortion in Mexico, according to public health experts. Abortion-rights activists say they are mainly sending medication north to help Americans rather than providing access in Mexico itself.

Luisa García, director of Profem’s clinics in Tijuana and Mexico City, said she would typically see only one patient a month crossing the border to Mexico, where clinics offer abortion care at a lower price than in the United States. But this year, she has received at least 80 calls from American numbers requesting appointments.

“I can’t believe it,” Ms. García said. “America was free and open-minded about abortion, but now with these decisions about the court, women need to relocate their reproductive and sexual rights.”

Ms. García said that Americans occasionally arrive at her clinic alone, nervous and speaking minimal Spanish. Some women have told her staff that they traveled to Mexico secretly without telling family members who disapprove of the procedure.

Nicole Huberfeld, a professor of health law at Boston University, said the decision to cross the border for abortions shows just how desperate many American women are to get the procedure.

“When we see more people crossing the border for care it shows something is wrong in the U.S.,” Ms. Huberfield said.

Mexican organizers say that even amid recent abortion-rights rulings in Mexico, the procedure is still not completely available nationwide. The Mexican Supreme Court ruling did not void criminal penalties at the local level, and private or state institutions can still ban the procedure.

Anti-abortion groups in Mexico adamantly opposed the top court’s decision this month.

Marcial Padilla, director of the Mexico-based ConParticipación, told the Catholic news agency ACI Prensa that Mexico’s Supreme Court decision would pressure senators to “remove the protection of the right to life.”

The recent court decisions in Mexico have conveyed “that a son or daughter does not deserve the same protection of the law before birth as after birth,” he said.

Some Americans seeking abortion care in Mexico were surprised to find lasting restrictions south of the border.

Vanessa Jimenez Ruvalcaba, a Mexican activist who opens her home in Nuevo León state near the border to women seeking abortions, received a call in July from a father who traveled to the state with his daughter from Nebraska, where abortion is banned after 12 weeks.

But Nuevo León only permits the abortion in the case of incest, rape or when the mother’s life is in danger. Ms. Jimenez said the father and daughter were turned away from a clinic before they were referred to her organization, the I Need to Abort Collective.

Ms. Jimenez and her fellow activists helped the young woman eventually access to abortion pills.

Even in the face of abortions bans, Mexican groups have formed a model known as “accompaniment,” in which they disseminate pills while providing medical counseling and psychological support to women.

Ms. Sanchez and her colleague, Carolina Castillo, said they have been implementing the model in Sonora for years. They are now fielding questions on social media from American women who fear facing criminal punishment for seeking abortion medication in the United States. They say the women are relieved to hear from organizers who have spent years confronting such restrictions.

“We have been living for many years in a context of social and legal penalization of abortion,” Ms. Sanchez said. “Which is why we, as women, have had to organize ourselves.”

Emiliano Rodríguez Mega contributed research from Mexico City.