Number Needed to Harm (NNH) is calculated from a drug trial where 8% of treated patients experience a severe adverse event versus 2% in the control group. What is the NNH?

• A 6
• B 12
• C 25
• D 17 ✓

Explanation

Absolute Risk Increase (ARI) = 8% − 2% = 6% = 0.06. NNH = 1/ARI = 1/0.06 = 16.7 ≈ 17. This means approximately 17 patients must be treated with the drug for 1 additional severe adverse event to occur. NNH is clinically compared against NNT to determine the benefit-to-harm ratio of a therapeutic intervention.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.