Side-effects of hydrocodone/paracetamol are most commonly upset stomach, nausea, and altered mental states (e.g., dizziness, light headedness). Other rarer side-effects include allergic reaction, seizures, clammy skin, paranoia, hallucinations, severe weakness, dizziness, hyperventilation, unconsciousness, jaundice (yellowing of eyes or skin), unusual fatigue, bleeding, bruising, stomach pain,[3] constipation, dry mouth, decreased appetite, muscle twitches, sweating, hot flashes, itching, tinnitus, hearing loss, decreased urination and altered sex drive. Vicodin also has depressant effects on the central nervous system, which may cause irritability. However, some of the less mundane effects can be desirable effects that are sought after by some. Those effects include euphoria and drowsiness, as well as slowing of the pulse.