Analgesic efficacy can be expressed as the number needed to treat" (NNT). Calculation of the NNT of a treatment involves assessing the number of patients who achieve a specific therapeutic target whilst allowing for those patients who received placebo who also reached that target. For analgesics used to treat acute pain, the target is usually the ability to reduce the pain by 50% or greater. It is notable that intramuscular morphine 10 mg has a higher NNT (that is lower efficacy) than a number of regularly used simple analgesics