Which symptom is a hallmark of excessive use of beta-agonists?

Tremors are a hallmark symptom of excessive use of beta-agonists. Beta-agonists, such as albuterol, are commonly used in the management of asthma and other obstructive airway diseases because they stimulate beta-2 adrenergic receptors, leading to bronchodilation. However, when used excessively, these medications can lead to systemic side effects due to overstimulation of these receptors in other tissues, particularly in the tremor-producing muscles.

The mechanism behind the tremors involves the activation of beta-2 receptors in skeletal muscle, which can increase muscle excitability and result in involuntary muscle contractions or shaking. This is a well-recognized side effect of beta-agonist therapy and can serve as a red flag for healthcare providers regarding the potential overuse of these medications, indicating that the patient's asthma control may not be adequate.

In the context of other symptoms, while fatigue, chest tightness, and persistent cough can occur in respiratory conditions, they are not as directly tied to the pharmacological effects of beta-agonists as tremors are. Therefore, tremors stand out as the classic symptom associated with excessive beta-agonist usage, making it the correct answer in this question.