Loopholes in state laws are allowing child marriage to flourish in the U.S., despite research showing that the practice puts young people at risk of serious, lifelong harm.

More than 200,000 children under 18 were married from 2000 to 2015 in the U.S., according to a report released Wednesday by the Tahirih Justice Center, a nonprofit organization working to end gender-based violence. The vast majority were underage girls who married adult men.

“America really does have a child marriage problem,” said Jeanne Smoot, author of the report. “It hurts children here, just as it does globally, and we are overdue to tackle it.”

While most states set a minimum age of 18 to marry, they typically allow exceptions if children have parental consent, or if a judge approves the union.

In recent years, advocates have lobbied for stricter laws on child marriage, with success. In 2016, Virginia enacted a law that limits marriage to those age 18 or older, with an exception for court-emancipated minors. This year, Texas and New York passed restrictions on child marriage.

But those are the only three states that limit marriage to legal adults. Startlingly, 25 states allow children of any age to be married, as long as exceptions are met. In Missouri, for example, children who are 15 or older can marry with parental consent. Children under 15 can marry with a judge’s approval. From 2000 to 2014, over 800 children age 15 or younger in Missouri were married using these exceptions.

The report highlights the challenges that child brides face ― and how difficult it can be for them to escape a marriage if they want to do so.

“The adult in these relationships typically holds all the cards and all the power,” Smoot said. “They know and manipulate the dependance of the child spouse, from the roof over their heads to a ride to the grocery store.”

Even in cases where children enter marriages voluntarily, the long-term consequences can be devastating, said Vivian Hamilton, a professor at William & Mary Law School who studies child marriage.

“Girls who marry in their teens are 50 percent more likely to drop out of high school, and they are four times less likely to finish college,” Hamilton said. “For girls who marry as minors, they are 31 percent more likely to live in poverty later than those who delay marriage.”

Individuals who marry young also suffer significantly more mental health problems, Hamilton added.

Child marriage can have multiple roots, said Fraidy Reiss, founder of Unchained At Last, a nonprofit dedicated to helping women and girls leave arranged and forced marriages.

In some cases, children may be pressured into it because of traditional or religious beliefs about premarital sex and pregnancy. In others, parents may not be able to provide for their child, and want to offload them to someone else. They could be motivated by a dowry, or want to control a child’s behavior or sexuality. They could be covering up a rape that ended in pregnancy.

“From our experience, when a child is forced into a marriage, the perpetrator is almost always the parents,” Reiss said. “But these children are not all coming out of abusive, violent, dysfunctional homes. It’s often parents who think they are doing the best thing for their child.”

Reiss, a survivor herself, recently led an effort to collect comprehensive state data on child marriages. She shared her statistics with PBS’s “Frontline,” which expanded on her research.

A big problem with allowing a child to marry is that they don’t have the full legal rights of adulthood, Reiss said. Children are not automatically emancipated once married. Depending on the state, if a girl tries to leave the marriage, she may be taken into custody, treated as a runaway. It can be hard for minors to rent an apartment, or to qualify for a full-time job.

“Basic steps like retaining an attorney are difficult,” Reiss said.

Minors may also be at greater risk of domestic violence, due to the uneven power dynamic between a child and an adult. Women aged 16 to 24 experience the country’s highest rate of domestic violence.

“We know that not knowing where one would go is one of the main reasons that battered women stay with abusers,” said Smoot. “Imagine a girl who may have had to drop out of high school and may only be able to work a certain number of hours under state labor laws.”

The report points out that some minor children are allowed to marry adults before they can legally consent to sex. State laws “governing the age of consent and the minimum marriage age are strikingly inconsistent and suggest, in essence, that at least some of the underage marriages being approved by clerks and judges are between rapists and their victims,” the report notes.

Trevicia Williams, 47, knows firsthand what it’s like to go from child to wife in a single afternoon.

When she was 14, her mother picked her up from school and told her she was getting married that day. After a quick trip to a courthouse in Harris County, Texas, she was hitched to a 26-year-old ex-convict she barely knew.

Her mother never gave her a reason why she arranged the marriage, Williams said. As far as she could tell, her mother just didn’t want to look after her anymore. But Williams had no interest in being a wife. She was determined to finish her education. After she and her new husband moved 25 miles away from her school, she rode the city bus every day to take classes.

“Marriage was not something I had a concept of or really understood,” Williams said.

At 15, she got pregnant. Her husband was violent and abusive, she said, and their life together was traumatic and unstable. When she was 16, he went back to prison. That’s when she found an organization that helped her file for divorce.

Williams’ ordeal was decades ago, but child marriages in her state did not stop. According to the report, 40,000 children were married in Texas from 2000 to 2014, some as young as 12.

Williams lobbied for a Texas bill on child marriage that passed this year. The measure, effective Sept. 1, prohibits anyone under 16 from getting married.

“Children are not psychologically nor physically developed enough to endure the impact of this experience,” Williams said. “Child marriages hurt children. They miss out on so many valuable experiences that they can never get back.”

This article has been updated with more details from the Tahirih Justice Center report.