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Why Do I Take Lantus Insulin At Night?

Not sure about the weight gain, but I can answer as to its function.
Your body burns sugar all the time, even when you're asleep. During the day the sugar generally comes from what you eat (and you can inject a bolus short acting insulin to counteract that), but when you're fasting or at night then there's a (reasonably) steady supply from your liver, which also needs insulin. That's what your basal (lantus) is for.

As a T2, your body isn't processing sugar very well, and isn't producing enough (any?) insulin to do that processing. The basal is supplementing your own night time insulin production so that your blood sugar levels stay in the correct range.
 
Hi @anon125,
As @EllieM, says some insulin is needed day and night apart from at mealtimes.
If you google "Lantus insulin profile pictures' you can see a graph of Lantus' blood-sugar lowering action over time.
If you compare that to a graph of a short-acting insulin (Novorapid/Apidra/Fiasp) you will see how the short-acting ones have a relatively high peak action of 1 to 3 hours and are inactive after 6 hours or less.
By contrast Lantus has a low, 'flat' profile over 24 hours +. That is why it is prescribed once per day to provide a low level 'background action'. That low level action also makes it less likely to cause low blood sugars at night but a low blood sugar is still possible.
Some people are prescribed Lantus once daily in the morning, others once daily at night. I have heard that it often comes down to what the prescribing doctor has read about in regards to prescribing practice or what the original prescriber ordered.
I cannot however guess the exact reason that you were prescribed it at night.
 
Hi,

I can only guess the advice to dose basal at night is to coincide with a longer fasting period.
Waking hours it's assumed that the "suggested" standard "3 square meals" are around 4 to 5 hours apart...?
Which is where the bolus works on the spike from the meals..

Of course there is no "one size fits all." Just a guideline....
 
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