The Somogyi effect is a sudden swing to high glucose levels (hyperglycemia) after episodes of low glucose (hypoglycemia) during sleep. A patient may go to sleep with normal glucose levels, but levels may drop during the night and result in nocturnal hypoglycemia. This in turn may trigger the release of hormones, including glucagon, that signal the liver to secrete more glucose into the blood. If too much glucose is released into the bloodstream, a patient may awaken in a hyperglycemic state.

For people with diabetes, nocturnal hypoglycemia and the Somogyi effect can result from causes such as taking too much insulin or not following a prescribed diet.

Signs and symptoms of nocturnal hypoglycemia include excessive sweating, restless sleep and waking with a headache. Patients may also notice symptoms of hyperglycemia in the morning, which include excessive urination, thirst or hunger, as well as weakness, fatigue and blurred vision.

Treating and preventing the Somogyi effect requires preventing nocturnal hypoglycemia. After first consulting their physician, patients with diabetes may require changes to their diabetes management plan. This can include changes to diet and medications.