A new generation of synthetic drugs is presenting novel legal problems, reports the Wall Street Journal. Law-enforcers and prosecutors say the products’ shifting chemistry makes it difficult to win convictions. The drugs often are sold in packages labeled “bath salts.” When smoked, snorted, or injected, they can cause reactions including increased energy and euphoria similar to cocaine or ecstasy, or hallucinations, similar to LSD. The American Association of Poison Control Centers said 6,138 calls were made reporting abuse of synthetics in 2011, up from 302 calls the year before. In 2012, the call total dropped to 2,657. The Drug Enforcement Administration last year launched a sweep to charge sellers. To get a conviction, prosecutors must prove the drug was substantially similar to a specifically banned substance. Because synthetic drugs are created from chemicals in a lab, with nearly endless variations, tweaks to chemistry can keep them from automatically being considered analogues–chemical compounds banned because they are similar to prohibited drugs. “There’s no way that the DEA can keep up with the sophisticated chemists around the world who are making this stuff,” said Timothy Heaphy, U.S. attorney for the Western District of Virginia, whose office won a bath-salts conviction earlier this year–just the second such prosecution. .