What Should You Know Before Starting Insulin Therapy?
Starting insulin therapy requires education on injection technique, blood sugar monitoring, carbohydrate counting (for mealtime insulin), recognizing and treating hypoglycemia, sick day management, and safe insulin storage. Work closely with a certified diabetes care and education specialist who will guide you through these essential skills over multiple training sessions.
Beginning insulin can feel intimidating, but modern insulin pens with short thin needles have made injections much simpler and less painful than most people expect. Your diabetes care team will teach you proper injection technique: choosing an appropriate site (abdomen, thigh, or upper arm), cleaning the area, pinching the skin if needed, inserting the needle at a 90-degree angle, injecting the insulin, holding for 10 seconds before withdrawing, and rotating sites to prevent lipohypertrophy. Insulin pen needles are available in lengths from 4 mm to 12.7 mm; the ADA recommends 4 mm needles for most adults, which are inserted at 90 degrees without pinching.
Understanding your insulin regimen is critical for safe and effective use. Your doctor will explain which insulin you are taking (basal, bolus, or premixed), when to take it, how to adjust doses, and how food and activity affect your insulin needs. If you are starting basal insulin only (such as insulin glargine or degludec), you will typically take one injection at the same time each day. If starting a basal-bolus regimen, you will take long-acting insulin once daily plus rapid-acting insulin before meals, with the mealtime dose based on carbohydrate intake and current blood sugar. Learning carbohydrate counting is essential for accurate bolus dosing.
Emergency preparedness is non-negotiable when using insulin. Always carry glucose tablets or another fast-acting carbohydrate source. Wear medical identification indicating that you use insulin. Ensure family members, roommates, and close coworkers know how to recognize severe hypoglycemia and administer glucagon. Keep a glucagon emergency kit (injection or nasal spray) readily accessible and check expiration dates regularly. The ADA recommends that all insulin users have a prescribed glucagon product.
What Are the Different Types of Insulin?
Insulin is classified by how quickly it starts working and how long it lasts. The main categories are rapid-acting (lispro, aspart, glulisine — onset 10 to 15 minutes), short-acting (regular insulin — onset 30 minutes), intermediate-acting (NPH — onset 1 to 3 hours), and long-acting (glargine, detemir, degludec — onset 1 to 2 hours with 24 or more hour duration).
Rapid-acting insulin analogs revolutionized mealtime insulin therapy by closely mimicking the body's natural insulin response to food. Insulin lispro (Humalog), insulin aspart (NovoLog), and insulin glulisine (Apidra) begin working within 10 to 15 minutes of injection, peak at 1 to 2 hours, and last 3 to 5 hours. Ultra-rapid-acting formulations including Fiasp (faster-acting aspart) and Lyumjev (ultra-rapid lispro) begin working in as little as 2 to 5 minutes. These insulins should be injected immediately before or within 20 minutes of starting a meal. Inhaled insulin (Afrezza) provides needle-free mealtime coverage with an ultra-rapid onset of 12 minutes.
Long-acting basal insulins provide steady background insulin coverage that controls blood sugar between meals and overnight. Insulin glargine U-100 (Lantus) and its biosimilars provide approximately 24 hours of relatively peakless coverage. Insulin glargine U-300 (Toujeo) has a longer and flatter profile lasting up to 36 hours with less variability. Insulin degludec (Tresiba) has the longest duration at over 42 hours and the flattest profile, resulting in the lowest rates of nocturnal hypoglycemia among basal insulins. Insulin detemir (Levemir) provides 12 to 24 hours of coverage and is often given twice daily. NPH (neutral protamine Hagedorn) is an older intermediate-acting insulin that peaks at 4 to 8 hours and is still widely used globally due to lower cost.
Insulin degludec (Tresiba) demonstrated lower rates of nocturnal and severe hypoglycemia compared to insulin glargine in the SWITCH and BEGIN trials
What Is Basal-Bolus Insulin Therapy?
Basal-bolus therapy is the gold standard insulin regimen that best mimics the pancreas's natural insulin secretion pattern. It combines once or twice daily long-acting basal insulin to cover between-meal and overnight needs with rapid-acting bolus insulin before each meal to cover dietary carbohydrates and correct elevated blood sugar.
The basal component typically provides about 40 to 50 percent of total daily insulin needs. Long-acting insulins like glargine, degludec, or detemir provide a steady level of insulin that suppresses hepatic glucose production between meals and overnight. Basal insulin is titrated based on fasting blood sugar: the dose is adjusted every 2 to 3 days until the fasting glucose target (typically 80 to 130 mg/dL) is consistently achieved. The Treat-to-Target trial established that systematic basal insulin titration guided by fasting glucose can achieve A1C targets effectively in type 2 diabetes with acceptably low hypoglycemia rates.
The bolus component covers the glycemic impact of meals and corrects pre-meal hyperglycemia. Mealtime insulin doses are calculated using two formulas: the insulin-to-carbohydrate ratio (for example, 1 unit per 10 grams of carbohydrate) determines the meal dose, and the correction factor or insulin sensitivity factor (for example, 1 unit lowers glucose by 50 mg/dL) determines the correction dose when pre-meal glucose is above target. These individual ratios are determined by your healthcare team and refined based on blood sugar patterns. Modern insulin pumps and smartphone apps include bolus calculators that automate these calculations, reducing dosing errors and improving glycemic outcomes.
The Treat-to-Target trial showed that systematic basal insulin titration achieves A1C targets with low hypoglycemia rates
How Do Insulin Pumps and Automated Delivery Systems Work?
Insulin pumps deliver rapid-acting insulin continuously through a subcutaneous catheter, replacing multiple daily injections with programmable basal rates and on-demand meal boluses. Hybrid closed-loop systems combine a pump with a CGM and algorithm that automatically adjusts basal delivery based on glucose readings, significantly improving time in range.
Modern insulin pumps include the Tandem t:slim X2 with Control-IQ, Medtronic 780G, Omnipod 5 (tubeless patch pump), and Insulet's Omnipod GO. These devices hold a reservoir of rapid-acting insulin and deliver it through an infusion set with a tiny plastic cannula inserted under the skin, typically on the abdomen or upper buttock. The infusion set is changed every 2 to 3 days. Pumps offer several advantages over injections: programmable basal rates that can vary by time of day (for example, higher rates during dawn phenomenon hours), precise bolus dosing in increments as small as 0.025 units, temporary basal rate adjustments for exercise or illness, and built-in bolus calculators that track active insulin to reduce stacking errors.
Hybrid closed-loop systems represent the current state-of-the-art in insulin delivery technology. These systems receive continuous glucose data from a CGM sensor, run a control algorithm that predicts glucose trends, and automatically increase or decrease basal insulin delivery to keep glucose in target range. Users still need to enter carbohydrates for meal boluses, which is why they are called hybrid (not fully) closed-loop. Clinical trials of hybrid closed-loop systems have demonstrated significant improvements: time in range increases of 10 to 15 percentage points, A1C reductions of 0.3 to 0.5 percentage points, and substantial reductions in hypoglycemia compared to sensor-augmented pump therapy. The NEJM published evidence that these systems improve outcomes in both adults and children with type 1 diabetes.
Clinical trials showed hybrid closed-loop systems increase time in range by 10 to 15 percentage points with reduced hypoglycemia
What Are the Side Effects and Risks of Insulin Therapy?
The most significant risk of insulin therapy is hypoglycemia, which ranges from mild symptoms to life-threatening emergencies. Other side effects include weight gain (typically 2 to 4 kg), injection site reactions, lipohypertrophy at overused injection sites, and rarely, allergic reactions. Understanding and preventing these risks is essential for safe insulin use.
Hypoglycemia is the primary safety concern with insulin therapy. The risk varies by insulin regimen: basal insulin alone carries lower hypoglycemia risk than basal-bolus therapy. Modern insulin analogs (glargine, degludec, lispro, aspart) cause less hypoglycemia than older insulins (NPH, regular). The DCCT found that intensive insulin therapy tripled the rate of severe hypoglycemia compared to conventional therapy, though the benefits in complication reduction far outweighed this risk. Strategies to minimize hypoglycemia include using CGMs with low glucose alerts, selecting insulin analogs with lower hypoglycemia risk, matching insulin doses carefully to carbohydrate intake, adjusting doses for exercise, and avoiding alcohol on an empty stomach.
Lipohypertrophy — rubbery lumps of fat that develop at repeatedly used injection sites — affects up to 50 percent of insulin users and is the most common injection-related complication. Insulin injected into lipohypertrophic tissue is absorbed erratically, causing unpredictable blood sugar fluctuations. Prevention requires strict injection site rotation using a systematic pattern. When switching away from a lipohypertrophic site to healthy tissue, insulin absorption improves, often requiring a 10 to 20 percent dose reduction to avoid hypoglycemia. Weight gain with insulin therapy can be managed by combining insulin with weight-neutral or weight-loss-promoting medications like metformin or GLP-1 receptor agonists.
The DCCT showed that intensive insulin therapy tripled severe hypoglycemia rates but dramatically reduced microvascular complications
How Is Insulin Used in Type 2 Diabetes?
In type 2 diabetes, insulin is typically added when non-insulin medications cannot achieve glycemic targets, when A1C is above 10 percent at diagnosis, or during acute illness, surgery, or pregnancy. Most patients start with basal insulin added to existing oral medications. Intensification to basal-bolus therapy may be needed as the disease progresses.
The ADA and EASD consensus recommends considering insulin therapy for type 2 diabetes when A1C exceeds 10 percent, when symptoms of hyperglycemia are present regardless of A1C, or when non-insulin medications at maximum tolerated doses do not achieve the individualized A1C target. Basal insulin is typically the first insulin prescribed, added to metformin and potentially other oral or injectable agents. Starting doses are usually 10 units per day or 0.1 to 0.2 units per kilogram of body weight, with patient-directed titration of 2 units every 3 days until fasting glucose reaches target. This approach, validated in multiple clinical trials, is safe and effective.
If basal insulin alone does not achieve the A1C target (especially if postprandial glucose remains elevated), intensification options include adding a GLP-1 receptor agonist (which has been shown to be at least as effective as adding bolus insulin with the advantage of weight loss), adding rapid-acting insulin before the largest meal (basal-plus regimen) and expanding to full basal-bolus if needed, or switching to premixed insulin formulations that combine basal and bolus components. The choice depends on patient preference, lifestyle, hypoglycemia risk, weight concerns, and cost. Fixed-ratio combinations of basal insulin with GLP-1 agonists (Soliqua, Xultophy) simplify therapy and provide complementary mechanisms of action.
What Is the Proper Technique for Insulin Injection?
Proper injection technique ensures consistent insulin absorption and reduces complications. Use 4 mm pen needles at a 90-degree angle for most adults. Rotate injection sites systematically within the same body region. Do not inject into lipohypertrophic areas, scars, or bruises. Leave the needle in the skin for 10 seconds after injecting to prevent insulin leakage.
The ADA and Forum for Injection Technique recommend these steps: wash hands, select the injection site, ensure the insulin is at room temperature (cold insulin stings), if using a pen attach a new needle for each injection, prime the pen by dialing 2 units and ejecting into the air, dial the prescribed dose, pinch the skin if using needles longer than 4 mm (not necessary with 4 mm needles), insert the needle at a 90-degree angle with a dart-like motion, press the plunger fully, count to 10 slowly before withdrawing, and remove the needle without rubbing the site. Use a new needle for each injection to prevent lipohypertrophy, infection, and injection pain.
Injection site rotation is critical for consistent insulin absorption. The abdomen provides the most consistent and fastest absorption, making it preferred for rapid-acting insulin. Divide each injection area into quadrants and move to a new spot within the quadrant for each injection, spacing injections at least 1 centimeter apart. Move to a new quadrant each week. Avoid injecting within 2 inches of the navel, into areas of visible veins or moles, or into lipohypertrophic tissue. For long-acting basal insulin, the injection site matters less because absorption is designed to be slow and steady regardless of location. However, use the same general body region (for example, always the thigh for basal insulin) at the same time of day for consistency.
What Does the Future of Insulin Therapy Look Like?
The future of insulin therapy includes fully closed-loop artificial pancreas systems, once-weekly basal insulins (insulin icodec), glucose-responsive smart insulins that activate only when blood sugar rises, implantable insulin delivery systems, and stem cell-derived beta cell replacement therapies that may eliminate the need for external insulin in type 1 diabetes.
Insulin icodec, a once-weekly basal insulin developed by Novo Nordisk, has shown comparable glycemic control to daily insulin glargine in Phase 3 trials with similar hypoglycemia rates. If approved, it would reduce the injection burden from 365 to just 52 injections per year for basal insulin. Glucose-responsive or smart insulins are being developed that remain inactive in circulation and become active only when blood glucose rises, potentially eliminating hypoglycemia risk entirely. Several approaches are in preclinical and early clinical development, using glucose-binding molecules that control insulin release.
Fully closed-loop (artificial pancreas) systems that require no carbohydrate input from the user are advancing in clinical trials. Dual-hormone systems that deliver both insulin and glucagon are being tested and may further reduce hypoglycemia risk. Beta cell replacement approaches include encapsulated islet transplantation using stem cell-derived beta cells, which would eliminate the need for immunosuppression, and gene therapy approaches to protect remaining beta cells or convert other cell types into insulin-producing cells. While many of these technologies are years from widespread availability, they represent a transformative trajectory toward increasingly automated and physiological insulin delivery.
Phase 3 trials of insulin icodec demonstrated comparable glycemic control to daily insulin glargine with once-weekly dosing
