What adulterants are commonly found in pills sold as Ecstasy?

The best place to find information on most substances found in ecstasy is www.ecstasydata.org, run by Erowid and partially funded by DanceSafe.

A large variety of substances are found in pills sold as Ecstasy. However, some show up more often than others.  For instance, opiates are rarely seen while caffeine and amphetamines are common. Piperazines like BZP and TFMPP are also showing up more and more often in the US, following the trends in Europe.