## **Core Concept**
Beta agonists are a class of medications that stimulate beta-adrenergic receptors, leading to various physiological effects. They are commonly used in the treatment of asthma, chronic obstructive pulmonary disease (COPD), and other conditions. However, like all medications, beta agonists can cause adverse effects.

## **Why the Correct Answer is Right**
The correct answer, **tachycardia**, is a well-known adverse effect of beta agonists. Beta agonists stimulate beta-1 receptors in the heart, leading to an increase in heart rate (tachycardia), contractility, and cardiac output. This effect is due to the activation of **Gs proteins** coupled to beta-1 adrenergic receptors, which increases intracellular cyclic AMP (cAMP) levels, enhancing cardiac electrical activity and contractility.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Hypotension is not typically an adverse effect of beta agonists; instead, they can cause hypertension due to increased cardiac output and peripheral vasoconstriction (though the effect on blood pressure can vary).
- **Option B:** Bronchoconstriction is the opposite of what beta agonists are used for; they cause **bronchodilation** by stimulating beta-2 receptors in the lungs.
- **Option C:** Decreased respiratory rate is not an effect of beta agonists; they can actually increase respiratory rate as a reflex response to decreased airway resistance.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **beta-2 selective agonists** are often used to minimize cardiac side effects (like tachycardia) while still providing bronchodilation. However, long-term use of beta agonists, especially non-selective ones, requires careful monitoring for cardiac effects.

## **Correct Answer:** D. Tachycardia