High blood sugar--abnormal, even dangerous levels of sugar in the blood--is known as hyperglycemia and is most often associated with the disease diabetes mellitus. However, different types of medications may also cause high blood sugar; this is sometimes known as medication-induced, or drug-induced, diabetes. Within the list of drugs are several medications that are used to treat depression. While only one medication is officially considered an "antidepressant," certain antipsychotics--which may also be used in the treatment of depression--may cause hyperglycemia as well.
Fluoxetine is a commonly-used antidepressant; it belongs to a class called the "serotonin-specific reuptake inhibitors," and may also be known by one of its brand names, Prozac. It is used to treat both depression that occurs as a result of major depressive disorder and, in combination with the antipsychotic medication olanzepine, to treat the depression that may occur in patients with bipolar disorder. In addition to its effects on blood sugar levels, fluoxetine may Medline Plus reports that fluoxetine can cause nausea, lack of appetite, weight loss, nervousness, and changes in sex drive. The medical reference UpToDate reports that in patients with diabetes, fluoxetine affects blood sugar regulation in an interesting way. Patients who take fluoxetine may have more episodes of hypoglycemia, or low blood sugar--but when they stop taking fluoxetine, instead of their blood sugar reaching normal levels, patients' blood sugar level goes above normal. This is called hyperglycemia, and this observation suggests that fluoxetine is somehow impacting the blood sugar regulation mechanism of patients with diabetes. Because of this, a patient who is taking medication for his diabetes and is also put on fluoxetine for depression, should be especially vigilant with checking his blood sugar levels. Changes to his diabetes medication, both while on fluoxetine and after fluoxetine is stopped, may need to be made to minimize the risk of hypo- and hyperglycemia associated with this medication.
Quetiapine is another member of the "atypical antipsychotics" category of medication. Similarly to its "cousin," olanzepine, quetiapine is used to treat depressive episodes that are associated with bipolar disorder--this is the disorder that was once called manic-depressive disorder and is characterized by recurrent episodes of mania and depression. It is also an "adjuvant" or supplement, therapy for major depression. This means that while quetiapine is not used as the only medication in treating patients with major depressive disorder, it may used in addition to another antidepressant to help relieve the symptoms associated with depression. The authors of "Pathogenesis of Type 2 Diabetes," written in the medical reference UpToDate, suggest that the risk of hyperglycemia in patients taking quetiapine is perhaps not as clear-cut as that in patients taking olanzepine. However, because there is a risk, and because this side effect can result in potentially fatal levels of blood sugar, it is important for patients with diabetes to take extra care in monitoring their blood sugar. Medline Plus, which is the health information website of the National Institutes of Health, list the possible side effects of quetiapine; these include dry mouth, dizziness, drowsiness, joint pain, and weakness.
Olanzepine is an atypical antipsychotic medication; however despite its pharmacological category, it is also used in the treatment of certain types of depression. Specifically, it may be used in patients who have depression associated with bipolar disorder; in cases of major depression that are not responding to other treatments, a combination of olanzepine with fluoxetine may be tried. According to the medical reference UpToDate, all atypical antipsychotic medications are associated with the potential for developing dangerously high levels of high blood sugar, but olanzepine may be more likely than other members within this category to cause this side effect. Because of this, patients who already have diabetes and are on this medication should be monitored carefully by their physician. Non-diabetic patients who are on olanzepine and have an increased risk for diabetes--for instance if they have a strong family history of Type 2 diabetes--should be monitored for the development of hyperglycemia with occasional checks of their fasting blood sugar. A fasting blood sugar level that is higher than normal is an indicator that diabetes may be developing due to the medication. Side effects, besides hyperglycemia, that may occur in patients taking olanzepine include extreme drowsiness, also called somnolence; dizziness; headaches; and weight gain.