Does Insulin Syringe Needle Length Matter?

When it comes to diabetes therapy, insulin is pharmacists’ most valuable weapon.

Although oral therapies can offer convenience and reduce hypoglycemia risk, the glucose-lowering effects of insulin remain unrivaled. Simply put, insulin is diabetic hormone replacement therapy. Patients with hypothyroidism receive levothyroxine, while patients no longer making sufficient insulin can replace it exogenously.

A variety of needle lengths are available, ranging from 4 mm to 12.7 mm

Unfortunately, patients may resist starting insulin for many reasons, one of which is a fear of needles. Injecting insulin can be painful, especially when using longer needles. Painful injections are not only unpleasant for patients, but can also lead to medication noncompliance and poorer health outcomes.

Although longer needles are often prescribed for patients with increased body fat, this practice actually has no clinical basis. Insulin is meant to be injected into subcutaneous tissue, human skin is only 1.6 mm to 2.4 mm thick, on average. Because skin thickness doesn’t increase significantly in overweight and obese patients, a 4-mm needle is sufficient to deliver insulin to subcutaneous tissue in patients of all sizes.

Furthermore, choosing longer needles can negatively impact therapy in thinner patients. If patients inject insulin intramuscularly because their needle is too long, the drug’s absorption will be accelerated, while it’s duration of action will be shortened.

Initiating insulin is often a significant lifestyle change for patients. Pharmacists can play a substantial role in helping patients overcome their fear of injection. For example, providing demonstrations and patient counseling about insulin—along with assuring patients that short-length, small-gauge needles can be used—can go a long way in promoting insulin acceptance and adherence.