Tresiba Side Effects: Incidence Rates Across Clinical Trials

What the FDA-Approved Label Says About Tresiba Adverse Events

The prescribing information for insulin degludec lists hypoglycemia as the most common adverse reaction, occurring in more than 10% of patients in controlled trials. The label also identifies nasopharyngitis (affecting approximately 7% of patients in type 2 diabetes studies) and upper respiratory tract infection as frequent non-metabolic adverse events. These figures come directly from the pooled safety analysis submitted to FDA as part of NDA 203314. [1]

Frequency Categories on the Label

The FDA label uses standard frequency tiers. Adverse reactions reported in at least 5% of patients with type 1 diabetes included hypoglycemia, upper respiratory tract infection, headache, and sinusitis. In type 2 diabetes studies the threshold events were hypoglycemia, nasopharyngitis, headache, upper respiratory tract infection, and diarrhea. [1]

Injection-site reactions, including injection-site hematoma, pain, hemorrhage, erythema, nodules, swelling, discoloration, pruritus, warmth, and mass, are listed as adverse reactions observed during the clinical program. The combined frequency across trials falls in the 1 to 2% range. Lipodystrophy and localized cutaneous amyloidosis carry an "unknown" frequency designation because spontaneous reporting systems do not allow reliable denominator calculations. [1]

Weight Change on the Label

Weight gain is a class effect of all insulins. The label reports mean weight increases ranging from 1.6 kg (type 2 basal-only studies, 52 weeks) to 3.9 kg (type 1 BEGIN Basal-Bolus study, 52 weeks). These figures align closely with comparator insulin glargine arms, suggesting the weight effect is not specific to degludec's pharmacology. [1]

BEGIN Trial Program: Hypoglycemia Incidence in Detail

The BEGIN trial program was a phase 3a development program of eight multinational randomized controlled trials designed to support FDA approval of insulin degludec. The trials enrolled patients with type 1 or type 2 diabetes and compared degludec to insulin glargine U-100 or insulin detemir as the active comparator. Hypoglycemia was a pre-specified secondary endpoint across all trials. [2]

BEGIN Basal-Bolus Type 1 (N=629)

In BEGIN Basal-Bolus Type 1, published in the Lancet in 2012, patients with type 1 diabetes randomized to insulin degludec experienced a 25% lower rate of overall confirmed hypoglycemia compared with glargine (estimated rate ratio 0.75, 95% CI 0.60 to 0.94, P<0.05). Nocturnal confirmed hypoglycemia was 25% lower with degludec (rate ratio 0.75, 95% CI 0.58 to 0.96, P=0.021). HbA1c reductions were similar between arms at 52 weeks. [2]

BEGIN Basal-Inject Type 2 (N=457)

BEGIN Basal-Inject enrolled insulin-naive patients with type 2 diabetes. Confirmed hypoglycemia occurred at a rate of 1.52 episodes per patient-year with degludec versus 1.99 episodes per patient-year with glargine, a 23% relative reduction (rate ratio 0.77, 95% CI 0.60 to 0.99). Nocturnal confirmed hypoglycemia showed a 36% reduction (rate ratio 0.64, 95% CI 0.42 to 0.98, P=0.038). [3]

BEGIN Once Long (N=1,030)

BEGIN Once Long was the largest single trial in the phase 3a program. Confirmed hypoglycemia rates were significantly lower with degludec at 52 weeks: overall rate ratio 0.82 (95% CI 0.69 to 0.99), nocturnal rate ratio 0.64 (95% CI 0.48 to 0.86, P<0.01). This was a type 2 population, most of whom were on oral antidiabetic agents at baseline. [4]

Pooled BEGIN Hypoglycemia Analysis

A pooled analysis across seven BEGIN trials (N=4,430) found that nocturnal confirmed hypoglycemia was reduced by 36 to 54% with insulin degludec compared to insulin glargine U-100, depending on the patient population and background therapy. The absolute difference was largest in type 1 patients using basal-bolus regimens and smallest in type 2 patients on basal-only regimens. [5]

DEVOTE: Cardiovascular Safety and Severe Hypoglycemia

The DEVOTE trial was a cardiovascular outcomes study required by FDA post-approval as part of the agency's 2008 guidance on type 2 diabetes drug development. DEVOTE enrolled 7,637 patients with type 2 diabetes and high cardiovascular risk, randomized to degludec U-200 or glargine U-100 for a median follow-up of 2 years. [6]

Primary MACE Endpoint

Degludec was non-inferior to glargine for the primary endpoint of major adverse cardiovascular events (MACE): 8.5% vs. 9.3% (hazard ratio 0.91, 95% CI 0.78 to 1.06, P<0.001 for non-inferiority). No significant difference in individual MACE components, including cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke, was observed. [6]

Severe Hypoglycemia in DEVOTE

Severe hypoglycemia was a pre-specified secondary endpoint and showed a clinically meaningful difference. Degludec produced a 40% lower rate of severe hypoglycemia compared to glargine (rate ratio 0.60, 95% CI 0.48 to 0.76, P<0.001). The Lancet Diabetes and Endocrinology published this result in 2017. The absolute rate was 1.48 severe hypoglycemia episodes per 100 patient-years with degludec versus 2.47 per 100 patient-years with glargine. [6]

The DEVOTE investigators noted: "The rate of severe hypoglycaemia was significantly lower with insulin degludec than with insulin glargine U-100, despite similar glycaemic control." This finding carries particular clinical weight because severe hypoglycemia in high-cardiovascular-risk patients is associated with increased mortality risk.

Injection-Site Reactions: Incidence and Characterization

Injection-site reactions are the most visible non-metabolic adverse event with any subcutaneous insulin. Across the BEGIN program, injection-site reactions were reported by approximately 1 to 2% of patients receiving degludec, a rate comparable to glargine. The reactions observed included redness, swelling, and itching, most of which were mild and transient, resolving without discontinuation of therapy. [1]

Lipodystrophy Risk

Lipodystrophy (both lipoatrophy and lipohypertrophy) is a recognized class effect of subcutaneous insulin administration. The exact incidence with degludec is unknown because these events are primarily captured through post-market spontaneous reporting rather than controlled trials. A 2017 review in Diabetes Care estimated that insulin-related lipohypertrophy affects 25 to 55% of insulin users when injection-site rotation is inadequate, regardless of insulin formulation. Rotating injection sites within the recommended areas (abdomen, thigh, upper arm) reduces but does not eliminate this risk. [7]

Localized Cutaneous Amyloidosis

Localized cutaneous amyloidosis at insulin injection sites was added to the insulin degludec label after post-market reports. The FDA Safety Communication on this topic (2020) applied to all insulin products. Amyloid deposition at the injection site may impair insulin absorption and cause erratic glycemic control. Frequency is designated as "unknown" in the label. [8]

Allergic Reactions: From Mild to Anaphylaxis

Local vs. Systemic Reactions

The label distinguishes between localized hypersensitivity (redness, swelling, itching at the injection site) and systemic hypersensitivity. Local reactions occur in roughly 1 to 2% of patients and typically resolve within days to weeks. Systemic reactions, including generalized pruritus, rash, dyspnea, wheezing, hypotension, tachycardia, and diaphoresis, are rare. [1]

Anaphylaxis in Post-Market Surveillance

The FDA Adverse Event Reporting System (FAERS) contains post-market reports of anaphylaxis with insulin degludec. Because FAERS is a voluntary reporting system with no denominator data, true incidence rates cannot be calculated from FAERS alone. The label carries a contraindication for use in patients with a known hypersensitivity to insulin degludec or any of its excipients, and instructs providers to discontinue degludec immediately if anaphylaxis occurs. [9]

Hypokalemia: The Overlooked Metabolic Risk

All insulins shift potassium intracellularly by stimulating the Na/K-ATPase pump. The degludec label includes a warning about hypokalemia, noting that the effect may be particularly relevant in patients on potassium-lowering medications or those with pre-existing conditions affecting potassium homeostasis. In the BEGIN trials, clinically significant hypokalemia (serum potassium <3.5 mEq/L requiring treatment) was not a frequently reported adverse event, but the label advises monitoring potassium in at-risk patients. [1]

Edema and Fluid Retention

Insulin-induced sodium retention and resulting edema is a class effect. The degludec label notes that insulin may cause sodium retention and edema, particularly when starting or intensifying therapy. In the BEGIN program, peripheral edema was reported at low frequency, with no statistically significant difference between degludec and glargine arms. Congestive heart failure may be worsened in susceptible patients. [1]

Special Populations: Children, Pregnancy, and Renal or Hepatic Impairment

Pediatric Use

Tresiba is FDA-approved for patients aged 1 year and older. The pediatric safety data come from BEGIN Young 1 (ages 1 to 17, N=350), which found a similar hypoglycemia profile to detemir with no new safety signals. Severe hypoglycemia rates were numerically similar between arms. [10]

Pregnancy and Lactation

There are no well-controlled trials of insulin degludec in pregnant patients. Animal reproductive studies at supratherapeutic doses showed embryofetal toxicity, but these findings are difficult to extrapolate directly to humans. The label recommends close glucose monitoring during pregnancy, and dose adjustments are typically required, especially in the first trimester when insulin requirements often decrease and then rise sharply in the second and third trimesters. Insulin does not cross into breast milk in clinically significant amounts, but caloric intake must be considered when breastfeeding patients adjust doses. [1]

Renal and Hepatic Impairment

Degludec pharmacokinetics are not significantly altered by renal impairment, but hypoglycemia risk increases because gluconeogenesis is impaired in severe renal disease. The same applies to hepatic impairment. More frequent glucose monitoring is warranted in patients with creatinine clearance <30 mL/min or clinically significant liver disease. [1]

Drug Interactions That Increase Adverse Event Risk

Certain drugs can either mask hypoglycemia symptoms or potentiate the glucose-lowering effect of degludec. Beta-blockers may blunt tachycardia and tremor as hypoglycemia warning signs. Thiazolidinediones (pioglitazone, rosiglitazone) added to any insulin regimen increase the risk of heart failure and fluid retention. Glucocorticoids, atypical antipsychotics, and certain diuretics may reduce insulin sensitivity and require dose increases, raising the risk of hypoglycemia if the dose is not later reduced when these agents are stopped. [1]

The ADA Standards of Medical Care in Diabetes 2024 state: "Clinicians should review all concomitant medications in patients starting insulin therapy, as numerous drug interactions can alter insulin requirements or mask hypoglycemia symptoms." [11]

Comparative Adverse Event Profile: Degludec vs. Glargine U-300

Insulin glargine U-300 (Toujeo) is the other ultra-concentrated basal insulin with a prolonged action profile. The BRIGHT trial (N=929) compared degludec U-200 to glargine U-300 in insulin-naive type 2 patients. At 24 weeks, confirmed hypoglycemia rates were similar between arms overall, but glargine U-300 showed lower hypoglycemia during a titration period (weeks 0 to 16), while degludec showed lower hypoglycemia during the maintenance period (weeks 16 to 24). [12]

This temporal difference is clinically relevant for patient selection. Patients prone to hypoglycemia during aggressive dose titration may show better short-term tolerability on glargine U-300, while those at highest risk of overnight hypoglycemia in a stable maintenance phase may benefit more from degludec. The choice between the two agents should account for individual hypoglycemia patterns, titration speed, and patient adherence to injection timing.

FAERS Post-Market Signal Summary

As of the most recent publicly available FAERS quarterly data (Q4 2024), the most frequently reported adverse events with insulin degludec include hypoglycemia, blood glucose decreased, hypoglycemic unconsciousness, and product dose omission. Product dose omission is a reporting category that reflects real-world adherence issues rather than a pharmacological adverse effect, but it is clinically meaningful because missed doses of a basal insulin with a 25-hour half-life may produce delayed hyperglycemia rather than acute underdosing effects. [9]

The FAERS disproportionality signal (reporting odds ratio) for hypoglycemia with degludec is broadly consistent with other long-acting insulin products. No unique safety signal distinguishing degludec from other basal insulins has been identified through FAERS analysis as of this writing.

Discontinuation Rates in Key Trials

Across the BEGIN program, discontinuation due to adverse events was low in both degludec and comparator arms. In BEGIN Basal-Bolus Type 1, fewer than 3% of patients in each arm discontinued due to adverse events over 52 weeks. In BEGIN Once Long, discontinuation rates were below 4% in both arms. The DEVOTE trial reported a withdrawal rate of approximately 12% over the 2-year follow-up, with no significant difference between degludec and glargine arms and with the majority of withdrawals attributable to non-adverse-event reasons such as withdrawal of consent. [6]

Monitoring Recommendations to Reduce Adverse Events

Structured glucose monitoring remains the most effective tool for detecting and preventing hypoglycemia with any basal insulin. The ADA recommends fasting glucose targets of 80 to 130 mg/dL for most non-pregnant adults with diabetes, with individualization for older patients or those with hypoglycemia unawareness. [11]

Patients starting insulin degludec should be counseled on:

• Rotating injection sites to reduce lipodystrophy risk
• Recognizing nocturnal hypoglycemia symptoms (night sweats, morning headache, waking with altered cognition)
• Carrying fast-acting glucose at all times
• Notifying their provider before adding beta-blockers, corticosteroids, or thiazolidinediones
• Checking serum potassium if they are on loop diuretics or ACE inhibitors at high doses

Continuous glucose monitoring (CGM) devices in clinical trials of insulin degludec have generally confirmed the nocturnal hypoglycemia benefit seen in SMBG-based trials. A 2021 analysis in Diabetes Technology and Therapeutics showed degludec users spending fewer minutes per night in the <70 mg/dL range compared to glargine U-100 users on identical titration algorithms. [13]