## **Core Concept**
The question tests knowledge of the side effects associated with salbutamol, a commonly used short-acting β2-adrenergic receptor agonist (SABA) in the management of asthma and chronic obstructive pulmonary disease (COPD). Salbutamol works by stimulating β2 receptors in the lungs, leading to bronchodilation. However, its use can be associated with various side effects due to its mechanism of action.

## **Why the Correct Answer is Right**
Salbutamol's most unpleasant side effect is tremors. This is because salbutamol, despite being selective for β2 receptors, can still stimulate β1 receptors to some extent, especially at higher doses. β1 receptors are found in the heart, but β2 receptors are also present in skeletal muscle, where their stimulation leads to tremors. This effect is due to the increased muscle contraction force and rate.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Not specified, but if related to common side effects like tachycardia or palpitations, these are less frequently the most unpleasant for patients compared to tremors.
- **Option B:** Not specified, but if related to other side effects like dry mouth or metallic taste, these are not typically highlighted as the most unpleasant.
- **Option C:** Not specified, but if related to hypokalemia or other metabolic effects, while important, these are usually not as immediately distressing as tremors.
- **Option D:** Not specified, but presumably another side effect; without specifics, it's hard to address directly.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while tremors are a common and sometimes dose-limiting side effect of salbutamol, they often decrease in frequency and severity with continued use. However, for patients, especially those with asthma or COPD who may already be anxious about their breathing, tremors can be particularly distressing.

## **Correct Answer:** D. tremors