Like all medicines, this medicine can cause side effects, although not everybody gets them.
Very common (may affect more than 1 in 10 people):
Drowsiness and constipation, dry mouth
Common (may affect up to 1 in 10 people):
Dizziness, headache, pupil contraction, nausea and vomiting, loss of appetite, indigestion or discomfort, changes in taste and smell, urticaria, sweating, bronchospasm, decreased coughing, asthenia
Uncommon (may affect up to 1 in 100 people):
Facial flushing, itching, spasms in the lower urinary tract, abnormal liver tests
Rare (may affect up to 1 in 1,000 people):
Increase in pancreatic enzymes (seen in a blood test) and inflammation of the pancreas, pain because of kidney stones (renal colic) or gallstones (biliary colic), withdrawal symptoms, orthostatic hypotension (a form of low blood pressure that happens when you stand up from sitting or lying down)
Very rare (may affect up to 1 in 10,000 people):
Difficulty breathing, muscle cramp, seizures, burning and stinging pain, increased sensitivity to pain, blurred vision, double vision, involuntary movement of the eye, a condition where the bowel does not work properly (ileus), abdominal pain, rash, swelling of the hands, ankles or feet, feeling unwell, shivering, syndrome of inappropriate antidiuretic hormone (SIADH) (symptoms: nausea, malaise, headache, exhaustion and in severe cases may progress to seizures and coma), absence of menstrual bleeding.
Not known (frequency cannot be estimated from the available data):
Adrenal insufficiency (fatigue, weight loss, fainting, low blood sugar, nausea, diarrhea, vomiting and abdominal pain), Euphoria (strong sense of well-being, happiness and excitement), uncontrolled muscle movements, addiction, dysphoric mood (sad, without energy), restlessness, decreased libido or potency, hallucinations, vertigo and fever.