SSRIs are a class of drugs (including Prozac, Zoloft and Paxil) which are used as prescription antidepressants. Functionally, they increase the levels of serotonin in the body. These drugs can be dangerous if they're mixed with other drugs such as other antidepressants, illicit drugs (LSD, cocaine, methamphetamine), some antihistamines (Seldane, Histmanal), some antibiotics, and calcium channel blockers.
Side effects include lethargy, confusion, flushing, sweating and muscle spasms. Overdose can cause damage to red blood cells, breathing problems and kidney damage.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.