The deltoid muscle has a triangular shape and is easy to locate and access, but is commonly underdeveloped in adults. Begin by having the patient relax the arm. The patient can be standing, sitting, or lying down. To locate the landmark for the deltoid muscle, expose the upper arm and find the acromion process by palpating the bony prominence. The injection site is in the middle of the deltoid muscle, about to 5 cm (1 to 2 inches) below the acromion process. To locate this area, lay three fingers across the deltoid muscle and below the acromion process. The injection site is generally three finger widths below, in the middle of the muscle.
Products may contain impurities developed in the production stage due to probably lack of hygiene in illegal drug factories. In addition, the active ingredients and their amounts are most likely to differ from the package label promises.
Furthermore, these products have also revealed traces of medicinal substances and other harmful ingredients previously removed from the market for safety purposes. In the manufacturing may have been used construction industry substances as a substitute for the correct medicinal substances, for example. Illegal substances may cause symptoms such as allergic reactions. 
If you see blood when you pull back on the plunger, you have probably hit a vein or artery. Withdraw the needle and begin again with a new needle, new dosage of medication and a new site. For your own safety, have a professional nurse or doctor instruct you on the proper method of giving a B12 injection and have her watch you do it the first time. If you give an injection in the buttock, make sure it is high and on the outside of the buttock, as the sciatic nerve runs down the center of the buttock, and you do not want to injure that main nerve.