Like all medicines, these tablets can cause side effects, although not everybody gets them.
The most serious side effect is a condition where you breathe more slowly or weakly than expected (respiratory depression). Tell your doctor immediately if this happens to you.
All medicines can cause allergic reactions, although serious allergic reactions are rare. Tell your doctor immediately if you get any sudden wheeziness, difficulties in breathing, swelling of the eyelids, face or lips, rash or itching especially those covering your whole body.
This table lists the most common side effects. To find out about less common side effects read section 4 of the package leaflet that comes with your medicine.