Intramuscular injection (referred to as intramuscular injection) is a common clinical route of drug administration, which refers to the injection of drug solution into the muscle tissue through a syringe to achieve the purpose of cure. It is mainly used when: intravenous injection is inappropriate or cannot be done, when more rapid therapeutic effect is required than subcutaneous injection, and when injecting drugs that are more irritating or in larger amounts. The most commonly injected part is the gluteus maximus, followed by the gluteus medius, gluteus minimus, lateral femoral muscle and its upper arm deltoid. The most common adverse reactions to intramuscular injections are allergic reactions to the “local” skin, manifested by redness, swelling, itching, pain, sclerosis, and liquefaction (necrosis) of subcutaneous fat at the injection site. “Severe rashes can spread all over the body, manifesting as large erythema, edema, and even blistering and erosion, and sometimes suffocation, vomiting, abdominal pain, and shock when shortness of breath, shortness of breath, decreased blood pressure, rapid pulse rate, and excessive sweating occur. This is mainly due to the patient’s reaction to the drug itself. This is mainly due to the patient’s allergic reaction to the drug itself, mostly related to the patient’s allergic constitution. With the continuous improvement of in vitro fertilization-embryo transfer (IVF-ET) technology, progesterone oil intramuscular injection has been widely used as a post-IVF-ET luteal support drug. Progesterone is usually started intramuscularly on the day of egg retrieval or at the time of embryo transfer and lasts for 12-14 days or until the onset of menstruation. If the pregnancy test is positive, progesterone therapy can be continued until 30 days after embryo transfer until a fetal heart is seen or maintained until 12 weeks of gestation. Why does progesterone intramuscular injection cause such adverse reactions? Our section according to years of clinical experience summed up the following points: a, drug factors Progesterone belongs to the oil injection, its oil molecules particles surface tension, difficult to be dissolved, tissue absorption is slow, easy to cause the accumulation of drug in the tissue. Second, injection factors 1, after repeated injections of local muscle stimulation, long time in the same part of the repeated injection needle stimulation damage, muscle fibers gradually atrophy degeneration; 2, receive injections when the spirit of excessive tension, muscle can not relax; 3, needle piercing depth is not enough, and the injection of the drug into the fat layer, because there are fewer blood vessels, not easily absorbed by the tissue, so that the injection site in the phenomenon of hard knots; 4, The amount of drug given each time is too much, more than 5mL increases the chance of forming hard knots. Physical factors 1. When patients are bedridden for a long time, their muscle activity is relatively reduced, and the blood supply to local tissues is also reduced, so that the absorption of drugs becomes slower and hard nodes are gradually formed. 2.People with scars, allergies and immune abnormalities.