Like all medicines, Zaponex can cause side effects, although not everybody gets them.
Very common (may affect more than 1 in 10 people):
Drowsiness, dizziness, increased production of saliva.
Common (may affect up to 1 in 10 people):
High level of white blood cells (leukocytosis), high level of a specific type of white blood cell (eosinophilia), weight gain, blurred vision, headache, trembling, stiffness, restlessness, jerks, abnormal movements, inability to initiate movement, inability to remain motionless, changes in ECG heart readings, high blood pressure, faintness or light-headedness after changing position, nausea (feeling sick), vomiting (being sick), loss of appetite, dry mouth, minor abnormalities in liver function tests, loss of bladder control, difficulty in passing urine, tiredness, fever, increased sweating, raised body temperature, speech disorders (e.g. slurred speech).
Uncommon (may affect up to 1 in 100 people):
Lack of white blood cells (agranulocytosis), speech disorders (e.g. stuttering).
Rare (may affect up to 1 in 1,000 people):
Low level of red blood cells (anaemia), restlessness, agitation, confusion, delirium, inflammation of the heart muscle (myocarditis) or the membrane surrounding the heart muscle (pericarditis), fluid collection around the heart (pericardial effusion), high level of sugar in the blood, diabetes mellitus, raised levels of an enzyme called creatinine phosphokinase in the blood.
Very rare (may affect up to 1 in 10,000 people):
Increase in numbers of blood platelets with possible clotting in the blood vessels, uncontrollable movements of mouth/tongue and limbs, obsessive thoughts and compulsive repetitive behaviours (obsessive compulsive symptoms), skin reactions, swelling in front of the ear (enlargement of saliva glands), difficulty in breathing, complications due to uncontrolled blood sugar (e.g. coma or ketoacidosis), very high levels of triglycerides or cholesterol in the blood, stopped heartbeat (cardiac arrest), sudden unexplained death.
Not known (frequency cannot be estimated from the available data)
Liver disorders including fatty liver disease, death of liver cells, liver toxicity/injury, liver disorders that involve replacement of normal liver tissue with scar tissue leading to loss of liver function, including those liver events leading to life-threatening consequences such as liver failure (which may lead to death), liver injury (injury of liver cells, bile duct in the liver, or both) and liver transplant, changes in brain waves readings (electroencephalogram/EEG), diarrhoea, stomach discomfort, heartburn, stomach discomfort after a meal, muscle weakness, muscle spasms, muscle pain, stuffy nose, nocturnal bedwetting, sudden, uncontrollable increase in blood pressure (pseudophaeochromocytoma), uncontrolled bending of the body to one side (pleurothotonus), ejaculatory disorder if you are a male, in which semen enters the bladder instead of ejaculating through the penis (dry orgasm or retrograde ejaculation), rash, purplish-red spots, fever or itching due to inflammation of blood vessel, inflammation of the colon resulting in diarrhoea, abdominal pain, fever, change in skin colour, “butterfly” facial rash, joint pain, muscle pain, fever and fatigue (lupus erythematous), restless legs syndrome (irresistible urge to move your legs or arms, usually accompanied by uncomfortable sensations during periods of rest, especially in the evening or at night and temporarily relieved by movement).
In elderly people with dementia, a small increase in the number of people dying has been reported for patients taking antipsychotics compared with those not taking antipsychotics.