

Unless you want to pay Heath Ledger a visit, don't mix ecstasy with energy drinks.

Researchers at Trinity College in Dublin, Ireland have gathered more evidence that the club drug and caffeine are a horrible combination. Their report will appear in the March issue of European Neuropsychopharmacology, but it is already available online.

Previously, Andrew Harkin and his colleagues showed rats

develop a dangerously rapid heartbeat when they are given MDMA along with the everyday stimulant. In their latest work, they verified that the blend of chemicals makes the lab animals feverish as well.

To test their theory, the scientists injected the drugs into Sprague Dawley rats and then probed them with a rectal thermometer. When the unlucky critters received both chemicals, their body temperatures increased far more than when they were given MDMA or caffeine alone.

Harkin and his team followed up with some very thorough work in an attempt to understand how the two chemicals interact. By giving rats a combination of caffeine and other drugs that have well-known effects on the brain, they were able to conclude that dopamine receptors, a type of nerve signaling protein, play a big role in the unusual overheating.