Which sign or symptom is MOST likely an adverse effect of diuretic medication?

The most likely adverse effect of diuretic medication is electrolyte imbalance with fatigue. Diuretics are commonly prescribed to help eliminate excess fluid by increasing urine output, which can lead to the loss of not only water but also important electrolytes such as potassium, sodium, magnesium, and calcium. An imbalance in these electrolytes can lead to symptoms like fatigue, muscle weakness, and cramping, amongst others. This makes option B particularly relevant as it directly addresses the common complication resulting from diuretic use.

While fluid depletion can occur with diuretics, the context of experiencing shortness of breath, as suggested in another option, may not be the most immediate or common adverse effect associated specifically with diuretic use. The fatigue often reported by patients is a clearer indicator of the underlying issue of electrolyte disturbances that diuretics can cause.