The Situation -- Sued for Hiding Rx Drug Addiction

The Situation was supposed to be the face of some anti-fat cream, but instead he ended up in rehab and never did a thing ... so says the company who hired him ... and now they want their $$$ back, this according to a new lawsuit.

A company in FL called Performance Brands claims they signed a deal with the "Jersey Shore" star back in September 2011 to endorse their fat metabolizing cream ... a job Sitch is perfect for thanks to his six-pack.

According to legal docs, PB claims they paid Sitch and his people a $75,000 advance. His job was to provide promotional material, give shout-outs on social media and make personal appearances ... which PB claims NEVER happened.

Not only that, PB says right after they sent the $$$ ... Sitch checked into rehab for a prescription drug addiction ... which they claim his PR team lied to them about, before later copping to the truth.

They say his failure to disclose his drug addiction is a breach of contract and they want all their money back.

Sitch fired back at the company with his own counter-suit -- claiming PB failed to give him a marketing plan on-time, advertise in national magazines, or give him free product. PB denies all these claims.