I.M. use only stands for Intramuscular use only, meaning the substance (such as a medication, steroid, or supplement) is intended to be injected directly into the muscle tissue, rather than intravenously (into a vein) or subcutaneously (under the skin).
Intramuscular injections are typically administered into larger muscles, such as the gluteus, thigh, or deltoid muscles, as these areas have a higher blood flow, allowing for the slow and consistent absorption of the substance into the bloodstream. It is important to follow the instructions for I.M. use only, as injecting the substance in any other way could lead to complications or reduced effectiveness.