Insulins are categorized first by length of action, then by origin and by suspension. The four durations are: 
|Rapid-acting or Fast-acting insulin begins to work shortly after injection, peaks in about 1 hour, and continues to work for 2 to 4 hours.|
|Regular or Short-acting insulin reaches the bloodstream 30 minutes to an hour after injection, peaks anywhere from 2 to 3 hours after injection, and is effective for approximately 6-8 hours.|
|Intermediate-acting insulin generally reaches the bloodstream about 1-2 hours after injection, and is effective for about 8 to 12 hours.|
|Long-acting insulin generally reaches the bloodstream about 2 to 4 hours after injection, peaks 4 to 8 hours later and is effective for about 12 to 18 hours.|
The article Insulin has more details.
The following insulins have articles of their own:
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