MDPV (also known as methylenedioxypyrovalerone):
is a psychoactive drug with stimulant properties. It has been sold since 2008 as a research chemical. In 2010, it began being sold as a legal drug alternative in the United States, marketed as bath salts in gas stations and convenience stores with similar marketing as Spice and K2 incense. It is sometimes called PV or PeeVee.
Mephedrone (also known as 4-methylmethcathinone or 4-MMC):
is a synthetic stimulant manufactured in China and is similar to the cathinone compounds found in the khat plant of eastern Africa. This is why bath salts are also referred to as plant food. Users can swallow, snort, or inject the chemical to produce similar effects to MDMA, amphetamines, and cocaine. It became available for sale on the Internet in 2007. In the U.K., it was sold in a product called bubbles (similar to bath salts). Street names include meow meow, Miaow, and M-Cat.
For more information http://www.ncfop88.org/bath_salts_0311.pdf