The opioid epidemic is leading to an increase in the number of “sober homes,” a form of housing where people in recovery live together in a supervised, substance-free setting. Most of these homes have little or no government oversight, the Associated Press reports.

Sober homes are rarely run by credentialed professionals, according to the AP. They often are run by people in recovery themselves who have remained clean after going through rehab.

At least five states have passed or are considering legislation to improve rules on the operation of these facilities. Some measures would require sober homes to be inspected and certified, and be subject to consumer protections and ethical codes. Some sober homes have been accused of insurance fraud and tolerating drug use.

“The ones that are good are fantastic,” said Pam Rodriguez, CEO of Treatment Alternatives for Safe Communities, an Illinois nonprofit that works to reduce prison time for nonviolent drug offenders. She noted the field also includes “people exploiting the vulnerability of the population and their desperation to find a safe place to live.”

Sober homes originally were designed as halfway houses for people in recovery from alcoholism. Now many sober homes cater to people trying to recover from opiate addiction. Some sober homes are single-family houses in residential neighborhoods, while others are apartment complexes.

Residents of sober homes range from people who recently were released from prison or residential treatment, to those who regularly see a counselor or who are not receiving any treatment. They are expected to participate in 12-step meetings and observe rules and curfews.

While there is no national estimate of the number of sober homes, experts tell the AP the number is growing. Oxford House, a network of sober homes, has almost 2,000 houses in about 500 cities—up 20 percent in the past three years.