Short answer: Low blood sugar (hypoglycemia) is the most common Lantus side effect, as with all insulin. In the label's trials against NPH insulin, other common reactions were upper respiratory infections (22.4% vs 23.1% in type 1, 11.4% vs 13.3% in type 2), other infections and headache, at similar rates on both. Injection site pain was 2.7% vs 0.7%. Lantus has no boxed warning.
What Lantus is approved for: Lantus is a long-acting human insulin analog approved to improve blood sugar control in adults and children with diabetes (section 1). It is not recommended for treating diabetic ketoacidosis.
Source
LANTUS (insulin glargine) injection, for subcutaneous use, prescribing information, Patient Information and Instructions for Use. Sanofi-Aventis U.S.. DailyMed, version published July 2, 2025. DailyMed setid d5e07a0c-7e14-4756-9152-9fea485d654a
No. The current Lantus label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Lantus.
| Adverse reaction | LANTUS, % (n=1,257) | NPH, % (n=1,070) |
|---|---|---|
| Upper respiratory tract infection | 22.4 | 23.1 |
| Infection | 9.4 | 10.3 |
| Accidental injury | 5.7 | 6.4 |
| Headache | 5.5 | 4.7 |
Studies A to D, compared with NPH insulin rather than placebo. Infection means body system not specified.
| Adverse reaction | LANTUS, % (n=849) | NPH, % (n=714) |
|---|---|---|
| Upper respiratory tract infection | 11.4 | 13.3 |
| Infection | 10.4 | 11.6 |
| Retinal vascular disorder | 5.8 | 7.4 |
Studies E to G, compared with NPH insulin. Infection means body system not specified.
| Adverse reaction | LANTUS, % (n=514) | NPH, % (n=503) |
|---|---|---|
| Upper respiratory tract infection | 29.0 | 33.6 |
| Edema peripheral | 20.0 | 22.7 |
| Hypertension | 19.6 | 18.9 |
| Influenza | 18.7 | 19.5 |
| Sinusitis | 18.5 | 17.9 |
| Cataract | 18.1 | 15.9 |
| Cough | 12.1 | 7.4 |
A 5-year study against NPH insulin; rates are over the full 5 years. The full table also lists bronchitis, joint pain, limb pain, back pain, urinary tract infection, diarrhea, depression and headache at 10.3% to 15.2% on Lantus.
| Study | LANTUS | NPH |
|---|---|---|
| Study A, adults, 28 weeks, with regular insulin (N=292 vs 293) | 10.6 | 15.0 |
| Study B, adults, 28 weeks, with regular insulin (N=264 vs 270) | 8.7 | 10.4 |
| Study C, adults, 16 weeks, with insulin lispro (N=310 vs 309) | 6.5 | 5.2 |
| Study D, pediatrics, 26 weeks, with regular insulin (N=174 vs 175) | 23.0 | 28.6 |
Severe symptomatic hypoglycemia means needing another person's help, with blood glucose below 50 mg/dL or prompt recovery after carbohydrate, glucose or glucagon. Values are percent of patients.
| Study | LANTUS | NPH |
|---|---|---|
| Study E, adults, 52 weeks, with oral agents (N=289 vs 281) | 1.7 | 1.1 |
| Study F, adults, 28 weeks, with regular insulin (N=259 vs 259) | 0.4 | 2.3 |
| Study G, adults, 5 years, with regular insulin (N=513 vs 504) | 7.8 | 11.9 |
Values are percent of patients. The 5-year study used a glucose cut-off of 56 mg/dL or less.
Table 7, ORIGIN study (median 6.2 years): severe symptomatic hypoglycemia in 5.6% on Lantus (N=6231) vs 1.8% on standard care (N=6273).
Table 4, children with type 1 diabetes over 28 weeks (Lantus vs NPH): infection 13.8% vs 17.7%, upper respiratory infection 13.8% vs 16.0%, pharyngitis 7.5% vs 8.6%, rhinitis 5.2% vs 5.1%.
Injection site pain was reported in 2.7% of adults on Lantus vs 0.7% on NPH insulin; it did not lead anyone to stop treatment.
Rapid improvement in blood sugar has been linked to a temporary, reversible vision refraction change, worsening of diabetic retinopathy and acute painful nerve pain. Weight gain and swelling from sodium retention can also occur.
Reported after approval: mix-ups where other insulins were given instead of Lantus, and localized cutaneous amyloidosis (lumps under the skin) at injection sites.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not use it. Lantus is not used during an episode of low blood sugar, or by people allergic to insulin glargine or its ingredients.
Never share pens, needles or syringes. A Lantus SoloStar pen is never shared, even if the needle is changed, and vial needles and syringes are never reused or shared, because of the risk of passing on blood-borne infections.
Changes in insulin regimen. Changing insulin strength, maker, type, injection site or method can cause high or low blood sugar, so changes are made under close supervision with more glucose checks. Injecting into lumpy or thickened skin can raise blood sugar, and switching to normal skin can lower it suddenly.
Low blood sugar. Hypoglycemia is the most common reaction to insulin, and severe episodes can cause seizures or death. Lantus's long action may delay recovery from a low. Awareness of lows may be reduced with long diabetes, nerve damage, beta-blockers or repeated lows.
Medication mix-ups. Mix-ups between insulin products have been reported, so the insulin label is checked before each injection.
Serious allergic reactions. Severe, life-threatening whole-body allergy, including anaphylaxis, can occur; Lantus is stopped if it does.
Low potassium. All insulins shift potassium into cells and can cause low potassium, which untreated can cause breathing paralysis, heart rhythm problems and death.
Heart failure with TZDs. Thiazolidinediones (such as pioglitazone) with insulin can cause fluid retention that may lead to or worsen heart failure.
From the Patient Information that comes with Lantus:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.