Get emergency medical help if you have signs of an allergy reaction to Lantus: redness or swelling where an injection was given, itchy skin rash over the entire body, trouble breathing, fast heartbeats, feeling like you might pass out, or swelling in your tongue or throat.
Call your doctor at once if you have:
weight gain, swelling in your hands or feet, feeling short of breath; or
signs of low potassium - leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.
Common Lantus side effects may include:
low blood sugar;
itching, mild skin rash; or
thickening or hollowing of the skin where you injected the medicine.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Lantus side effects (more detail)
Before taking this medicine
You should not use Lantus if you are allergic to insulin, or if you are having an episode of hypoglycemia (low blood sugar).
Lantus is not approved for use by anyone younger than 6 years old, and should not be used to treat type 2 diabetes in a child of any age.
To make sure Lantus is safe for you, tell your doctor if you have:
liver or kidney disease; or
low levels of potassium in your blood (hypokalemia);
Tell your doctor if you also take pioglitazone or rosiglitazone (sometimes contained in combinations with glimepiride or metformin). Taking certain oral diabetes medicines while you are using insulin may increase your risk of serious heart problems.
Tell your doctor if you are pregnant or breastfeeding.
Follow your doctor's instructions about using Lantus if you are pregnant or you become pregnant. Controlling diabetes is very important during pregnancy, and having high blood sugar may cause complications in both the mother and the baby.
