Injection of almost any drug or solution into the muscles of a food animal will result in scar tissue formation and some residual lesion in those muscle tissues. These lesions are very displeasing to consumers if found in meat products. Their presence also contributes to loss of tenderness for much of the remainder of the cut of meat. If found during processing, the lesions can be trimmed out but this still results in trim loss and increased labor costs for the processor.
Bagley, Clell, "Video ordering information for Realizing the Impact of Injection Site Lesions" (2001). All Current Publications. Paper 420.