The UK’s Cambridge University announced its plans to pay cocaine and crack addicts to participate in a study on the impact of drugs on the brain. Participants will be given an MRI brain scan, fill out a questionnaire, take computerized assessments, and have their blood drawn for genetic analysis. There’s only one catch: Each addict must have a non-using brother or sister who is also willing to take part in the research.

An advertisement in a local paper doesn’t say how much volunteers will be paid, and the scientists behind the study refused to disclose the amount. People volunteering for similar tests in the past have received up to 300 pounds. Dr. Karen Ersche, the principle researcher, defended the compensation, explaining that it’s difficult to attract suitable volunteers.

"The advert deliberately mentions no amount because we do not want people to approach us just for the money," she said. "People who normally volunteer really want to find out about the brain. I will tell them how much they will get paid after we have discussed the project fully.”

Ersche continued, “What we are trying to discover is why some people are much more susceptible to drug addiction than others. Lots of people take cocaine but only 16 percent get addicted."

Researchers said that a small number of addicts had already responded to the advertisement. In 2007, Cambridge was criticized for paying addicts up to 100 pounds a day over three days for related research into the effect of drugs on the brain. Critics claimed that addicts could spend the money on illegal drugs, calling for the money to be given to charity.