Lantus (insulin glargine U100) and Toujeo (insulin glargine U300) were originally developed and studied as once-daily basal insulins. Regulatory trials were designed to demonstrate that a single daily injection could match the performance of older twice-daily basal insulins. While this helped with marketing and convenience, the physiology of insulin glargine actually tells a different story.

The half-life of Lantus is around 12 hours, and Toujeo around 14–18 hours (with large day-to-day and person-to-person variation). A medicine with this half-life will still release insulin slowly over time, but it means that for many people—especially those with higher insulin resistance—the effect does not reliably last a full 24 hours.

This is why many adults experience a “wear-off” effect: rising glucose in the late afternoon or early morning, despite taking their insulin at the same time each day. In these cases, a split (twice-daily) dose of Lantus or Toujeo often provides more stable cover. You can read more about how basal insulin works in our Lantus SoloStar guide and our overview of diabetes treatment.

Why once-daily was never physiologically ideal

Although once-daily injections were sufficient for regulatory approval, clinical experience and newer analyses show that many people—even on moderate doses—benefit from splitting basal insulin. A long-acting insulin works best when the injection timing matches the rise and fall of your liver’s glucose release. If half the insulin has worn off by early morning, fasting levels and late-day glucose often drift higher.

Why twice-daily Lantus or Toujeo can improve control

Splitting Lantus or Toujeo typically provides a more even 24-hour insulin profile, reducing the “weak spots” that appear when a single dose wears off too early. This is especially true when daily doses exceed 50 units, where absorption can become inconsistent if all units are injected at one site.

Toujeo and Lantus are the same insulin, but Toujeo is more concentrated. When injected into the fatty tissue under the skin, both form insulin crystals as they neutralise. With Toujeo, these crystals are more uniform in size, so they dissolve at a more predictable rate. With Lantus, the crystals vary more and therefore break down less consistently.

A useful analogy is thinking of ice blocks melting in a tub. If every block is the same size, they melt evenly. If some are large and some tiny, the melting becomes unpredictable. This difference in consistency explains why Toujeo has:

a smoother absorption curve
a longer duration of action
less person-to-person variability
fewer hypoglycaemia episodes in clinical trials

Toujeo vs Lantus: hypoglycaemia evidence

Across the EDITION clinical trial programme, Toujeo U300 produced approximately 20% fewer confirmed or severe nocturnal hypoglycaemia episodes compared with Lantus U100. These results were consistent across type 1 and type 2 diabetes populations.

Peer-reviewed summaries of these studies are available via PubMed: EDITION 1–3 trial data.

If you’d like to see how glargine compares with other basal insulins (such as degludec), you can explore our basal insulin comparison.

When should Lantus or Toujeo be taken twice daily?

Common reasons your diabetes team may recommend splitting your basal insulin include:

rising glucose in the late afternoon or early morning
the dose has reached 50 units or more
your injection time varies widely from day to day
shift work or irregular sleep patterns
recurrent early-evening hypos when injecting in the morning
large swings in fasting glucose despite dose adjustments

Typical ways to split the dose

Split-dose regimens vary, but common examples include:

50/50 split (half in the morning, half in the evening)
60/40 split if morning readings tend to rise
40/60 split if late-day glucose drifts high

Your diabetes team will help you decide which pattern fits your glucose data best. If you use a CGM, split dosing can dramatically flatten your overnight and daytime curve.

Morning vs evening dosing still matters

If you take the basal insulin in the morning, the peak effect often occurs in the earlier part of the day. When dose titration is based on fasting glucose, this can push the dose up, increasing the risk of late-evening hypos. Taking basal at night places the “peak” during the overnight fasting period, which is why most adults achieve more stable fasting results with an evening or bedtime regimen.

When to seek individual advice

You should speak with your diabetes specialist, GP, or educator if you are considering a split dose, especially if you:

are having repeated hypos
take steroids or have major lifestyle changes ahead
are pregnant or planning pregnancy
are switching between basal insulins
use more than one daily injection of rapid insulin

For more background, see our guides on dose titration and the type 1 diabetes hub or type 2 diabetes hub.

Once Daily vs Twice Daily Lantus or Toujeo: What’s the Best Dose Timing?