WEDNESDAY, May 25 (HealthDay News) -- The Internet has put the world at people's fingertips, but in some cases it has also allowed banned or controlled substances to slip within their grasp, British researchers warn.

Their new study, published online May 19 in Drug Testing and Analysis, looked at so-called "legal highs," where certain drugs sold online contain ingredients other than those claimed and can be hazardous. These products are quickly becoming big business for manufacturers and suppliers, who market them toward recreational drug users.

"It is clear that consumers are buying products that they think contain specific substances, but that in reality the labels are unreliable indicators of the actual contents," Dr. Mark Baron, of the School of Natural and Applied Sciences at the University of Lincoln in England, said in a news release from the journal's publisher.

Although these "legal highs" are often readily available for purchase on the Internet, they are potentially dangerous for consumers, the study authors pointed out. The investigators found that these drugs, sometimes marketed as bath salts or plant food, commonly contain controlled substances and are being sold illegally.

In investigating these drugs, Baron bought an array of pills from U.K. websites and analyzed their contents. Six out of seven products purchased did not contain the active ingredients advertised.

In fact, in five out of seven cases, the products actually contained a controlled substance combined with caffeine. Among them was benzylpiperazine, a stimulant drug that is illegal in the United States and can cause anxiety, increased blood pressure, rapid heart rate and blurred vision, among other side effects.

Although the United Kingdom and other governments have taken steps to crack down on these "legal highs," suppliers continue to market these drugs, side-stepping current regulations. As a result, Baron cautioned buyers to be wary of any products they buy online.

"No guidelines exist as to what is sold and in what purity, and consumers are led to believe that purchased goods are entirely legal," he said. "The product name cannot be used as an indication of what it contains as there is variation in the content of the same product name between different Internet sites," Baron added.

The findings should serve as a red flag for consumers, as well as the lawmakers attempting to curb the illegal sale of controlled substances, the study authors noted.

"As legislation deals with the current crop of products we can expect to see new products appearing that try to find a route of supplying previously banned substances," Baron warned.

More information

The U.S. Food and Drug Administration has more about controlled substances.