Explain why morphine is contraindicated in head injury ?

Head injury is a traumatic , painful condition requiring analgesic.

Morphine in opoid analgesic.

1-It depresses respiratory drive.slowing of respiration leads to retention of co2

which will lead to increased intracranial tension.Head injury itself increases intracranial tension.

2-Raised intracranial tension leads to vomiting. Morphine also stimulates CTZ , LEADING TO nausea and vomiting.

3–Head injury assessment is done by pupillary constriction /dilataion.

Morphiune interferes wih this assessment/prognosis because it causes pupillary miosis- constriction of pupil.