While the drug has many side effects, one of the more important ones is worsening blood glucose control. However, data on the effect of niacin on blood glucose control is not as plentiful as data on diuretics and beta-blockers. One well-controlled study of 148 people with diabetes evaluated the effects of several different doses of niacin on both blood lipids and blood glucose control. The goal of the study was to evaluate the common medical practice of avoiding prescribing niacin to people with diabetes. Fasting blood glucose levels as well as glycosylated hemoglobin (HbA1c, another measure of blood glucose control) levels were evaluated over a 16-week period. While the doses of 1,000 mg and 1,500 mg of niacin were effective for blood lipids, the higher dose resulted in an average increase in HbA1c of 0.3 percentage points, and four people on niacin left the study due to its worsening of blood glucose control. The conclusions of the study were that niacin can be safely used in people who have diabetes, but that once again, in select individuals it can have an adverse effect on blood glucose control.
In another study, niacin was tested in combination with simvastatin, another blood-lipid-lowering drug, in 160 people who had low HDL cholesterol but normal LDL cholesterol. The investigators looked mainly at the progression of lesions in coronary arteries, but they also evaluated blood glucose and insulin levels. Participants who received these two drugs demonstrated a significant reduction in coronary artery lesions and heart attacks. They also, however, had elevated insulin levels but not elevated blood glucose. This suggests that niacin may cause insulin resistance, a condition in which the body does not use insulin efficiently.
In a review article that examined trials of niacin for both cardiovascular benefits and risks pertaining to diabetes care, it was clear that niacin has significant and positive benefits for cardiovascular health (namely, reduced heart attacks) but that small increases in blood glucose and insulin levels occur that may require adjustments to diabetes therapy.
Antipsychotic drugs are used to treat severe psychiatric conditions such as schizophrenia. While schizophrenia is not a common disease among people who have diabetes, among people with schizophrenia, there is a 15% prevalence of diabetes and a risk of developing it two to three times that of the general population. Some of this risk may be due to family history, poor diet, and physical inactivity. But recent evidence suggests that some drugs used to treat schizophrenia may increase the risk of developing diabetes.
A consensus statement from the American Diabetes Association and the American Psychiatric Association recognizes that antipsychotic drugs, and in particular olanzapine and clozapine, can elevate blood glucose, cause weight gain, and increase blood lipids. These drugs also raise the risk for diabetic ketoacidosis, an uncommon but extremely serious complication of diabetes. Several hypotheses have been proposed regarding how these drugs may cause diabetes, from simply inducing weight gain to impairing insulin secretion; but so far, no strong evidence explains why these drugs have this effect.
Striking a balance
There is a longer list of drugs associated with diabetes, but the evidence for each of these is not very strong, or the medicine is only used rarely. For the more commonly used drugs that are known to worsen diabetes control, it is important to note that there remains a balance between intended benefits and unwanted side effects. Glucocorticoids can stop an inflammatory process like asthma, thiazide diuretics have been shown to be very successful at reducing high blood pressure and its complications, beta-blockers do protect against heart attacks, niacin does reduce coronary artery disease, and antipsychotic medicines can make the difference between hallucinating and perceiving reality.