Final answer:
Injecting substances into the DAOs or mentalis muscles, usually for cosmetic or therapeutic reasons, can lead to side effects such as bruising, swelling, asymmetry, and possibly muscle weakness if not done properly.
Step-by-step explanation:
The side effects of injecting drugs into the DAOs (Depressor Anguli Oris) or mentalis muscles largely depend on the substance being injected and the purpose of the injection. These muscles are located on the face; the DAOs muscle helps in controlling expressions related to frowning, and the mentalis muscle is located on the chin and helps in pouting the lips.
Common injections into these muscles involve neuromodulators like Botox for cosmetic reasons or therapeutic purposes. Potential side effects can include bruising, swelling, asymmetry, and less commonly, muscle weakness or difficulty in performing normal facial expressions when too much product is used or if it spreads to adjacent muscles.