The first drug-testing service licensed by the Home Office allowing users to have substances checked has opened.
The month-long pilot project in Weston-super-Mare offers anyone over 18 to have their drugs analysed anonymously at a clinic run by charity Addaction.
Roz Gittins, from Addaction, said: "If people know what's in something, they can be better informed about the potential harm of taking it."
The Home Office said it backed the plan to allow research to be carried out.
Testing the samples is expected to take about 10 minutes and users will be asked to fill in a questionnaire to "allow harm reduction advice to be tailored to their needs".
Ms Gittins said: "This is about saving lives. We know people take drugs. We don't have to condone it but nor should we judge people or bury our heads in the sand."
A Home Office spokesperson said: "Anyone interested in lawfully undertaking activities which include the possession, supply or production of controlled drugs (including potentially the service of drug testing) needs to apply for a licence. They would then be subject to the usual considerations, visits and fees.
"A Home Office licence (for one year) was issued so approved research could be undertaken in Addaction's clinic in Somerset in accordance with the terms of that licence."
The pilot is being run in partnership with Hertfordshire University, which is providing testing and advice, and not-for-profit group The Loop, which already tests drugs at music festivals.
It will be reviewed after a month.
Amira Guirguis, from the University of Hertfordshire, said: "The drug checking service reflects our research vision on improving the identification of the actual content in drug samples, identifying potential sources of severe harm, gaining an understanding of novel trends and raising relevant alerts."
Addaction said: "All partners involved in this pilot agree that they are not condoning the use of illegal drugs, and samples are not returned to their owners."