In medical terminology, injection is a parenteral (outside the digestive system) route of administration where a solution or suspension is administered to the body using a device called an injector (usually a combination of a syringe and an injection needle). This method aims to maximize the bioavailability of the drug, accelerate the onset of action, and deliver it directly to the target tissue. While orally administered drugs may be broken down in the gastrointestinal tract, experience absorption problems, or have delays in reaching the target area, needle injection overcomes these obstacles.

The fundamental principle of injection administration is to ensure the drug is absorbed at different rates depending on the site of administration. For example, if a drug needs to act quickly, it can be administered intravenously (into a vein), while if a slower and longer-lasting effect is desired, it can be administered subcutaneously (into adipose tissue). This variety provides flexibility in modern medicine’s drug delivery strategies.

The choice of injection needle is crucial, depending on the route of administration, the viscosity of the drug, and the patient’s age/body type. The correct injection needle size is a critical factor for both delivering the drug to the correct tissue and ensuring patient comfort.

Why Are Injections Given?

The reasons behind administering injections vary depending on the type of medication, the patient’s clinical condition, and the desired therapeutic effect. The main indications for injection therapy are:

**Requirement for Rapid Therapeutic Effect:** In emergency medical situations such as anaphylaxis, severe infections, or pain attacks, the medication needs to quickly enter the bloodstream and reach the target organs. Intravenous injection is ideal for this purpose.

**Medications That Cannot Be Administered Orally:** Some biological drugs, protein-based molecules, or substances that are broken down or not absorbed by digestive system enzymes can only be administered by injection. For example, insulin used in type 1 diabetes is necessarily given by subcutaneous injection because it is broken down in digestion.

**Localized Treatment:** When a specific area of ​​the problem needs to be directly targeted, such as inflammation in a joint or a muscle knot, the injection is given directly to that area to minimize systemic side effects. Epidural injections and intra-articular cortisone applications fall into this category.
Vaccinations: The vast majority of vaccines used to provide immunity against infectious diseases are administered by injection under the muscle or skin to activate the immune system.

Long-Lasting Effect: Some medications are prepared in depot form to eliminate the need for the patient to take medication every day and can be given intramuscularly at less frequent intervals, such as once a month.