Barcelona - Drug charity Energy Control says it has been forced to turn away drug-users hoping to have the quality of their street drugs tested.
Energy Control has been offering the free and anonymous service since 1997 as a way of helping to reduce the risks of recreational drug use.
In recent years its popularity has increased and now more than 5,000 samples are tested each year.
One drug user, who preferred to remain anonymous, told Al Jazeera he uses the service to determine if the drugs he buys on the street are safe to take.
“You can’t always trust who you are buying from," he says.
"It's not a market that’s controlled, so if I can have more information about what I am taking, I can decide if I want to take it or not.”
"The service is increasing year by year," lab coordinator Mireia Ventura told Al Jazeera.
"We are not able to analyse all the samples we receive so we need to make some limits."
Along with the free service operated out of its office in central Barcelona, Energy Control also receives samples through the post, for testing which users must pay for.
"Some people say we are promoting the use of drugs because [we] are giving a safe way to consume," says Ventura.
"But we are giving the results in a neutral manner and are detecting dangerous products. We are saving lives.”
More than 70 percent of the cocaine tested by the service is found to be cut with other ingredients.
Some of these are extremely toxic and include drugs intended for animals.
Last year Energy Control found that a pill with a "Superman" branding contained a lethal mix of a substance called PMMA.
An alert was raised across Europe, but not before a number of people died.
"One pill was enough to kill one life," says Ventura.
"We remove a lot of pills from the market. We only know of one death but we are sure that if it was not detected there would have been more."
The incident highlighted the importance of the service to both help protect drug-users from dangerous drugs and give scientists insight into the 30-40 new synthetic drugs hitting the street each year.
"Our contribution to society is to provide this kind of service free to consumers," Rafael de la Torre, toxicology professor and the Director of Neuroscience at the Hospital del Mar Medical Research Institute, told Al Jazeera.
"But on the other side it is a way of being aware of what is going on on the street, the trends in drug addiction and drug composition and things like that."
Scientists say it is often impossible to know just how dangerous the new drugs are and existing screening and testing techniques are too slow to be of much use.
That is why scientists are using data from the free testing service to develop a new way to predict the toxicity of new drugs.
"It takes too long. We have to find a new approach to evaluating them," says de la Torre.
"The idea of the project is to create a database of drugs that we know very well and include the new ones in a way that will give us their predictive toxicology.
"You enter the structure of the compound and the machine will be able to predict what will happen when you take [the drug]."
Source: Al Jazeera