The goal of this clinical trial is to learn if standard-dose methylprednisolone sodium succinate can improve neurological recovery and safety in adults with moderate to severe traumatic brain injury (TBI). The main questions it aims to answer are:

1. Does adding a 5-day course of methylprednisolone improve overall long-term neurological outcome compared with placebo?
2. Does methylprednisolone reduce 6-month mortality or increase the proportion of patients with good neurological recovery?
3. What medical problems do participants experience when receiving methylprednisolone? Researchers will compare methylprednisolone sodium succinate (2 mg/kg/day intravenously for 5 days) with a matching placebo to see if the steroid improves outcomes beyond standard TBI care.

Participants will:

1. Receive either methylprednisolone or placebo once daily for 5 days, added to guideline-directed standard care.
2. Undergo CT scans and neuro-examinations during hospitalization.
3. Return for follow-up visits at 1 month and 6 months after injury for neurological assessments, safety checks, and questionnaires.

Inclusion Criteria:

• Age 18-65 years.
• Patients with moderate-to-severe traumatic brain injury whose Glasgow Coma Scale (GCS) score at admission is 4-12.
• Study drug must be initiated within 12 hours after injury.
• Imaging (CT) demonstrates cerebral contusion, or cerebral contusion with intracerebral hematoma.
• Written informed consent obtained from the subject or legally authorised representative.

Exclusion Criteria:

• Known hypersensitivity to corticosteroids or any contraindication to their use.
• History of diabetes mellitus, or capillary blood glucose <2.8 mmol/L or >22.2 mmol/L.
• Shock at admission (systolic blood pressure <90 mmHg for more than 30 minutes).
• Pregnant or lactating women.
• Participation in another clinical trial within the past 3 months.
• Any condition that, in the investigator's opinion, renders the patient unsuitable for this study.