Aside from the known problems of psychiatric disorders, appetite suppression, and possible heart and brain damage associated with cocaine, users of the drug are increasingly at risk from substances added to it by dealers, a new study shows.

Energy Control, a Spanish NGO that offers free analysis of banned drugs, says that 91 percent of cocaine it tested over the course of last year had been cut. "It should be explained that, in general, those who bring their drugs to Energy Control do so because they are suspicious of the quality since they bought them from unknown sellers," Fernando Caudevilla, a doctor with the NGO, says.

One of the most common adulterants in cocaine is a substance called levamisole. This drug is dangerous primarily because it suppresses the immune system of those who are exposed to it.

Cocaine purity has stood at around 50 percent over the past decade

Over 60 percent of ecstasy doses tested lacked the active ingredient MDMA

Levamisole is an anti-parasitic used in large livestock and aquarium fish. Levamisole is also an antineoplastic - a drug that inhibits abnormal cell growth which can ultimately produce potentially malignant tumors - used in the treatment of colorectal cancer in human beings.

However, this use has been discontinued in the United States and many other countries. Side effects from therapeutic doses of levamisole include nausea, diarrhea, dermatitis, taste perversion, fatigue, vomiting and infection.

According to Energy Control, Levamisole is apparently present in some shipments of cocaine intercepted before they are broken up for further distribution to consumers. It seems possible it is more than simply a bulking agent.

One theory is that levamisole or other adulterants boost the effects of cocaine, permitting material to pass for higher-quality product despite additional cuts made down the line.

Another theory is that levamisole or other adulterants are added as chemical signatures used to track distribution of material. "It may be that levamisole has been used because it has similar solubility properties to cocaine and therefore is difficult to remove and has not previously been considered a serious health hazard," says Energy Control.

Although it has been used therapeutically in humans for decades, Levamisole can cause acute neutropenia, a blood disorder characterized by the disappearance of certain types of white blood cells necessary for the proper functioning of the immune system.

Neutropenia can result in a wide range of problems associated with a weakened immune system including infections throughout the body, high fever, chills, swollen glands, painful sores and wounds that don't heal.

Over the course of 2010, Energy Control tested 345 samples of cocaine, and found that 91 percent were adulterated, with 23.2 percent containing no cocaine at all. Barely 5 percent was pure cocaine. Levamisole was found in 59 percent of samples.

Interior Ministry data shows that cocaine purity has stood at around 50 percent over the last decade, while the price has stayed at around 55 eurosa gram.

The US Drug Enforcement Administration (DEA) first reported seeing significant amounts of levamisole-tainted cocaine in 2005, with 331 samples testing positive. Then the numbers spiked. The DEA found 6,061 tainted samples in 2008 and 7,427 in 2009. One DEA brief from 2010 reports that between October 2007 and October 2009, the percentage of seized cocaine bricks containing levamisole jumped from 2 percent to 71 percent.

Which is not only sudden, but odd. Levamisole is not like other common cutting agents - sugar, baking powder, laxatives, etc, in that it is more expensive than other cuts and is being cut into the cocaine before it hits the United States.

This last mystery is the most puzzling. Typically, smugglers like to move the purest possible product - less volume means less chance of detection - and cut their drugs once in the country they are to be sold in.

Energy Control's survey found that 61 percent of so-called ecstasy tablets contained no MDMA, the active ingredient in the drug. In powder form, known in Spain as crystal, the purity is higher. More than 68 percent of 515 samples contained pure MDMA, with no type of additive. A tablet costs between 5 eurosand 6 euros, and a gram of crystal around 55 euros.

More than 73 percent of amphetamine samples tested by Energy Control were adulterated, with just 1.2 percent pure. The most common diluting agent Energy Control found was caffeine. A gram of speed costs around ¤22. Around half of the samples it analyzed of Ketamine, an animal tranquilizer, were found to be pure.

Luis Bononato, a doctor who works with drug addicts in Cádiz, says that drug users must learn to understand that they are almost always likely to be taking adulterated substances. "Rather than telling people to take drugs in moderation, we need to get the message over that you are putting your life in somebody else's hands when you buy and take drugs," he says.

Rafael Guayta-Escolíes of the Observatory of Drug Abuse at the College of Pharmacy in Barcelona says there is no such thing as moderate drug use. "I don't think that responsible use exists. The line is so fine that it is non-existent. By definition drugs are chemicals that cause psychological, physical or social damage, and on that basis drug use can never be responsible," he says.