Paxil (paroxetine) is a common prescription anti-depressant drug; it is classed as a "selective serotonin reuptake inhibitor," or SSRI, which functionally means that it increases the levels of serotonin in the body.
This drug, as is the case with other SSRIs, 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.