Which condition is a contraindication for using metformin?

Metformin is contraindicated in patients with decreased renal function primarily due to the risk of lactic acidosis, a serious complication that can occur when metformin is administered in individuals with compromised kidney function. The kidneys play a crucial role in excreting metformin, and if renal function is impaired, the drug can accumulate in the body, increasing the potential for toxicity. Therefore, assessing kidney function before initiating metformin therapy is essential, and regular monitoring should continue throughout treatment.

In contrast, while diabetes type 1 may not respond favorably to metformin alone, it is not an absolute contraindication; metformin can sometimes be used in conjunction with insulin. Hypertension is a common comorbidity in patients with diabetes but does not contraindicate the use of metformin. Thyroid disorders also do not preclude metformin usage; however, care should be taken to monitor thyroid function if the patient is on thyroid hormone replacement. Thus, decreased renal function is the key factor that contraindicates the use of metformin based on the risks involved.