They vary in how long they last, how much of a peak they have, and when that peak occurs. The ranges that I gave in the table on page 244 are only an approximate guide. There is a big difference from one person to the next. Most people who take NPH insulin notice that it gives them a peak about six or eight hours after they take it and that the effect of any shot of NPH has mostly worn off by about twelve hours. Because of that, they need to make sure they have something to eat six or eight hours after they have taken it. They also need to take two shots a day. Some people like that peak. If they take NPH insulin in the morning before they leave for work, the peak of the NPH occurs in the middle of the day when they are going to eat lunch anyway. So they don't need to give themselves a shot of fastacting insulin before lunch. I have other patients who tell me that a single dose of NPH in the morning will last them all the way through to the next morning. That is uncommon but does occur.
Both Lantus and Levemir last longer than NPH. They also have smaller peaks. The drug companies that make these insulins like to advertise them as having no peak, but that is not always true. They also like to claim that these insulins last for a full twenty-four hours on a single shot. This is sometimes true, but not always.