Final answer:
A therapeutic response to methimazole in a client with hyperthyroidism would be indicated by a decrease in weight.
Step-by-step explanation:
A client with hyperthyroidism who has been taking methimazole for 6 months would show a therapeutic response to the medication if their weight is 1.4 kg (3.1 lb) less than baseline. Hyperthyroidism is characterized by an increased metabolic rate, weight loss, and increased heart rate. Methemazole is an anti-thyroid drug that helps decrease the production of thyroid hormones, so a decrease in weight would indicate that the medication is effectively controlling the overproduction of thyroid hormones and restoring the client's metabolic rate to a more normal level.