**Question:** Which of the following is not a side effect of amitriptyline:

A. Dry mouth
B. Constipation
C. Headache
D. Sedation

**Core Concept:** Amitriptyline is an antidepressant drug primarily used in the treatment of depression, anxiety disorders, and neuropathic pain. It belongs to the class of drugs known as tricyclic antidepressants, which work by blocking the reuptake of neurotransmitters like norepinephrine, serotonin, and dopamine.

**Why the Correct Answer is Right:** Dry mouth is a common side effect of amitriptyline, as it inhibits the reuptake of norepinephrine and serotonin, leading to dry mouth due to reduced salivary secretion. The other options are either direct physiological effects or common side effects related to the drug's mechanism of action:

- Constipation: Amitriptyline can cause gastrointestinal tract slowing, leading to reduced motility and thus constipation.
- Headache: Although amitriptyline can cause orthostatic hypotension, it is less likely to cause headache directly.
- Sedation: Similar to dry mouth, sedation is a common side effect due to reduced activity in the central nervous system (CNS).

**Why Each Wrong Option is Incorrect:**

- Headache is an indirect effect of amitriptyline, making it less likely compared to dry mouth and constipation, which are direct side effects.
- Sedation is a common side effect, while headache is less likely.

**Clinical Pearl:** Although headache is a known side effect of amitriptyline, it is less likely compared to its direct side effects like dry mouth and constipation. This is because headache is not a direct result of the drug's pharmacological action on neurotransmitter reuptake inhibition.

**Correct Answer:** C. Headache