Eyes, ears, nose, and throat
Pinpoint pupils
Gastrointestinal system
Constipation
Nausea
Spasms of the stomach or intestinal tract
Vomiting
Heart and blood vessels
Low blood pressure
Weak pulse
Nervous system
Coma
Drowsiness
Possible seizures
Respiratory system
Difficulty breathing
Slow and labored breathing
Shallow breathing
No breathing
Skin
Bluish-colored fingernails and lips
This is a list that you can find rather easily on the web (And quite possibly the search bar on this most informative site) but here is the morphine "Heavy dose" symptoms list.