Google began notifying addiction treatment providers last week that they're allowed to buy ads on the search engine's results pages, Behavioral Healthcare Executive reports.

It's been six months since the company pulled such ads worldwide because news investigations had found that advertisers were paid to funnel patients to sometimes shoddy facilities.

More than 100 addiction treatment centers have been cleared to join Google's AdWords service, David Khalaf, a spokesman for LegitScript, told Behavioral Healthcare Executive, an industry magazine. Earlier this year, Google hired LegitScript, a company that provides security services for online health businesses, to develop a method of vetting addiction treatment ads so that the company could start accepting the ads again, Reuters reported. LegitScript considers 15 criteria, including criminal background checks and checks for appropriate licenses. It charges would-be advertisers $1,995 a year for its services, according to Reuters.

The addiction treatment industry has received intense scrutiny over the past couple of years, as journalists have documented unscrupulous practices, such as patient brokering and the proliferation of call centers that appear to be neutral referral services, but actually receive per-head commissions from treatment facilities to send patients to them. In an investigative Congressional hearing last week, as Pacific Standard reported, industry heads denied their companies did anything wrong, but said they supported stronger regulation of their work.