Insulin Glargine

Is insulin glargine safe?

Yes, when the dose is right, and for many people with diabetes it is not optional. Insulin glargine is a long-acting "basal" insulin injected once a day. It has been sold in the US since April 2000, first as Lantus, and later as the stronger Toujeo and biosimilar versions such as Basaglar and Semglee. It has no boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary, and a six-year trial of 12,537 people found no extra heart or cancer risk.

The catch is the one every insulin shares: it lowers blood sugar whether or not you have eaten. Too much causes hypoglycaemia, which can lead to seizures or coma. That is why it scores 60, below tablets like metformin (80) that rarely cause lows on their own. A lower score here does not mean anyone should avoid or stop insulin they need; it reflects how carefully it has to be used.

How common is low blood sugar on glargine?

Very common in mild form, and not rare in severe form. The Lantus label counts "severe symptomatic hypoglycaemia", meaning an episode where someone else had to help:

Group (Lantus label)	Glargine	Comparison
Adults, type 1, 16 to 28 weeks	6.5% to 10.6%	5.2% to 15.0% on NPH insulin
Children, type 1, 26 weeks	23.0%	28.6% on NPH
Type 2, 52 weeks with tablets	1.7%	1.1% on NPH
ORIGIN, early type 2, 6.2 years	5.6%	1.8% on standard care

Rates are similar to older NPH insulin, so glargine is not a low-risk exception. In the US, insulin-related lows and errors led to about 97,600 emergency visits a year between 2007 and 2011, and almost a third of those people were admitted (Geller and colleagues, JAMA Internal Medicine, 2014). People aged 80 and over were nearly five times as likely to be admitted as those aged 45 to 64.

Mix-ups and dosing errors

The same study found that the most common triggers were eating less than usual and injecting the wrong insulin. The label warns about this directly: check the label every time. Common traps:

• Lantus vs Toujeo. Toujeo has 300 units/mL, Lantus 100 units/mL. The Lantus label says to start at 80% of the Toujeo dose when switching.
• Basal vs mealtime insulin. Injecting a full dose of a rapid-acting insulin instead of glargine at bedtime can cause a severe night-time low.
• Biosimilar switches. A change of brand, strength or device needs closer glucose checks for the first weeks, the label says.

Glargine must not be mixed with other insulins, diluted, used in a pump or injected into a vein. Pens must never be shared, even with a new needle, because of the risk of blood-borne infection.

Interactions that change your dose

Insulin interacts with physiology more than with specific chemistry, so the list is long. The label groups the main ones:

• Can push sugar down: other diabetes drugs (including semaglutide and tirzepatide), ACE inhibitors and ARBs, fluoxetine, fibrates, salicylates, sulfonamide antibiotics.
• Can push sugar up: steroids such as prednisone, diuretics, olanzapine and clozapine, thyroid hormone, oral contraceptives, salbutamol (albuterol).
• Either way: alcohol, beta-blockers, clonidine, lithium.
• Hide the warning signs: beta-blockers and clonidine can blunt shaking and a racing heart.

Supplements sold for blood sugar, such as berberine, can add to the effect; tell your prescriber about them.

How to stay safe

• Inject at the same time each day into the abdomen, thigh or upper arm, and rotate sites within the same area. The MHRA warned in 2020 that injecting into lumpy areas (lipodystrophy or amyloid deposits) can stop insulin working well, and switching suddenly to fresh skin can then cause a low.
• Carry fast-acting glucose and make sure family know how to use emergency glucagon.
• Check glucose more often when you are ill, exercising more, drinking alcohol, or starting or stopping other medicines.
• Glargine is not a treatment for diabetic ketoacidosis.
• Talk to your doctor or pharmacist before changing brand, strength or timing.

How we scored it

Track record (92) and regulatory warnings (80) are strong: 25 years of use, large outcome trials and no boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary. Dependence (90) is not a concern. The score is pulled down by overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (30), because a modest excess can cause a dangerous low, by frequent serious side effects (50) in the form of severe hypoglycaemia, and by the long list of interactions (55).