Which of the following is NOT a potential side effect of certain respiratory drugs?

The selected response identifies "Severe headache" as a side effect that is not commonly associated with respiratory drugs. Most respiratory medications, such as bronchodilators or corticosteroids, have different known side effects related to their mechanism of action—typically involving effects on respiratory function, heart rate, or electrolyte balance.

Conjunctivitis, cancer risk, and blurred vision can be side effects due to specific medications. For instance, certain systemic corticosteroids can lead to increased intraocular pressure or contribute to cataract formation, which in turn may cause blurred vision. Some respiratory medications, particularly those affecting the immune system or hormonal balance, have been linked to cancer risks. Conjunctivitis can be a side effect of various medications, including some that are used for chronic obstructive pulmonary disease (COPD) or asthma management, particularly in cases where the drug may cause dry eyes or allergic responses.

Thus, the identification of "Severe headache" as the correct response reflects an understanding that while headaches can occur as a symptom of underlying respiratory issues or secondary effects from other medications, they are not commonly categorized as a direct side effect of typical respiratory pharmacotherapy.