Answered 12/18/2014 by Samuel Grossman, BS Pharm, Pharm.D, CDE
Crystals inside the insulin pen may indicate that the medication will not work properly. When insulin is exposed to the cold, heat, or when the insulin expires, crystals may form. Sometimes there may be particles inside the insulin solution and a simple shake may dissolve this particles. If after a shake of the solution the particles are not dissolved, there may be a problem with that insulin inside the pen or the vial and it may not work properly. Using an insulin pen that does not work properly may not decrease blood sugar effectively and may lead to high blood sugar levels. I would recommend an additional shake (not vigorously). If the crystals do not dissolve, you may need to use a new insulin pen.