Conventional insulin therapy (CT) started in the 1930s, when long-acting insulins became available (see Knowledge about Insulins). These insulins were made using special substances such as NPH (Neutral Protamine Hagedorn) and Surfen to slow down how they worked.

At that time, the main goal was to reduce the number of injections needed. This helped avoid the pain caused by the thick, blunt needles used back then and reduced the effort of cleaning and sterilizing reusable glass syringes.
The focus wasn’t yet on adjusting insulin to a person’s daily routine — it was simply about keeping people with diabetes alive. More frequent blood sugar checks would have helped, but regular home blood glucose testing only became possible in the 1980s.

Why CT Leads to Poorer Blood Sugar Control

When the Diabetes Control and Complications Trial (DCCT) was published in 1993, it clearly showed that people with type 1 diabetes who used CT had much worse blood sugar control compared to those using multiple daily injections. This also meant a higher risk of long-term complications.

Because of this, CT is no longer recommended for people with type 1 diabetes.
However, it can still be used in special cases — for example, in people who can’t or don’t want to manage intensive therapy, such as those with limited mental abilities, people in nursing care who can’t receive several injections a day, or those who simply don’t want to inject more than twice daily.

Premixed Insulins Used in CT

Helpful clarifications & caveats

• What “ratio” means: it’s the percent of rapid/short-acting component vs. intermediate/basal component. For example, 30/70 = 30% rapid (e.g., regular or aspart/lispro) + 70% NPH or protamine-crystallized analog. (See U.S. labels for examples.) (FDA Access Data)
• Naming differences: In Europe, Humalog® premixes may be branded Liprolog® in some countries; product content is the same (insulin lispro/lispro protamine). (European Medicines Agency (EMA))
• Availability can change: e.g., Insuman® premixes have been withdrawn/discontinued in several EU markets; Ryzodeg® is EMA-authorized in Europe but not currently marketed in the U.S. despite historic FDA approval. Always verify locally. (diabetes.org.uk)

Less Flexibility in Daily Life

This type of therapy is simple in terms of insulin use — only two fixed injections per day at set times.
But managing it isn’t easy, because insulin levels don’t match how the body naturally releases insulin. In other words, the insulin acts at the wrong times compared to the body’s real needs.
This is clear when you compare CT insulin levels with natural insulin production.

People using CT also have to stick to strict meal plans, which makes everyday life less flexible for those living with diabetes.