The IM medical abbreviation means intramuscular, so a medicine marked IM is injected deep into a muscle. Muscles have a rich blood supply, which lets the drug move into the bloodstream over minutes to hours.
IM is one of the routes every pharmacy and nursing student learns early, alongside IV for into a vein and PO for by mouth. Many vaccines are given IM, as are some antibiotics, emergency medicines and long acting injections. In other settings IM can also mean internal medicine, the adult medicine specialty, or infectious mononucleosis. On an order next to a dose, though, it almost always means the route.
At a glance
Stands for
Intramuscular, into a muscleOther meanings
Internal medicine (specialty); infectious mononucleosisWord roots
Latin intra, within, and musculus, muscleCommon sites
Deltoid, thigh (vastus lateralis), hip (ventrogluteal)Where you see it
Vaccine records, medication orders, emergency notesDo not confuse with
IV (into a vein), subcut (under the skin), IN (intranasal)
What the IM medical abbreviation means for a dose
An intramuscular injection passes through the skin and the fat layer into the muscle below. The needle is longer than one used just under the skin, and the length is chosen based on the person's size and the site. The medicine forms a small pocket in the muscle and is absorbed from there.
That absorption is faster than a shot under the skin and slower than a drug put straight into a vein. It also lets some medicines be made as long acting forms that release slowly over weeks.
Reading an IM order
Clinic order: "Influenza vaccine 0.5 mL IM left deltoid x1." The vaccine is given once into the deltoid, the rounded shoulder muscle, on the left arm. x1 means a single dose.
Emergency note: "Ceftriaxone given IM, pt tolerated." The antibiotic was injected into a muscle rather than through a drip. Both lines show format only.
Volume limits vary by site and age, so a larger volume may be split or given in a bigger muscle. Nurses record the site, which helps if there is any reaction later and helps rotate sites for repeated injections.
Common injection sites
| Site | Where it is | Often used for |
|---|---|---|
| Deltoid | Upper outer arm | Most adult vaccines, small volumes |
| Vastus lateralis | Outer middle thigh | Infants and young children; also adults |
| Ventrogluteal | Side of the hip | Larger volumes in adults |
| Dorsogluteal | Upper outer buttock | Used less now because of nearby nerves and vessels |
IM compared with other injection routes
| Route | Where the drug goes | Speed of effect |
|---|---|---|
| IV | Straight into a vein | Fastest |
| IM | Into a muscle | Moderate |
| Subcut | Into fat under the skin | Slower |
| ID, intradermal | Into the skin layer | Slowest; used for skin tests |
The route is part of the order for a reason: some drugs are only safe by one route. ISMP's error-prone list names IN, for intranasal, since a hurried IN looks a lot like IM or IV, and it recommends writing intranasal or NAS instead. It also lists SC and SQ, so subcut is the safer written form for under the skin.
IM pharmacy abbreviation and the other meanings
As a pharmacy abbreviation, IM is always the route. In a referral letter or job title, IM usually means internal medicine, the specialty of doctors who care for adults, as in an IM clinic or IM resident. In older notes or lab requests you may also see IM for infectious mononucleosis, the viral illness often called mono. Context makes it clear: a dose and a site point to the route, while a department or diagnosis points elsewhere.
More route shorthand appears in the prescription abbreviations section, including SL for under the tongue.
How and where an injection should be given is decided by the person giving it and the prescriber. Questions about your own shots are best asked of your nurse or pharmacist.
Frequently asked questions
What is the IM medical abbreviation meaning on an order?
IM means intramuscular, so the medicine is injected into a muscle. The order often also names the site, such as the deltoid.
Is IM the same as IV?
No. IM goes into a muscle and is absorbed over minutes to hours. IV goes directly into a vein and acts almost at once.
Why are most vaccines given IM?
Muscle tissue has a good blood supply and many immune cells nearby, and IM vaccines tend to cause fewer local skin reactions than shots placed in the fat layer. Each vaccine's instructions set its route.
What does IM mean besides intramuscular?
It can mean internal medicine, the adult medicine specialty, or sometimes infectious mononucleosis. The surrounding words tell you which is meant.