**Core Concept**
Amitriptyline is a tricyclic antidepressant (TCA) with various side effects, primarily due to its anticholinergic and antihistaminic properties. The anticholinergic effects of TCAs can lead to autonomic dysfunction, manifesting as urinary retention, constipation, and blurred vision.

**Why the Correct Answer is Right**
Amitriptyline blocks the action of acetylcholine at muscarinic receptors in the central and peripheral nervous system, leading to anticholinergic side effects. This blockade results in decreased parasympathetic tone, causing urinary retention due to decreased detrusor muscle contractility and increased bladder neck tone. Similarly, constipation occurs due to decreased gut motility, and blurred vision results from decreased tear production and pupil dilation. The anticholinergic effects of amitriptyline are a major contributor to its side effect profile.

**Why Each Wrong Option is Incorrect**
**Option B:** Expressed symptoms of depression are unlikely to cause urinary retention, constipation, and blurred vision. While depression can have various physical manifestations, these specific symptoms are more related to autonomic dysfunction than emotional or psychological distress.

**Option C:** Superadded prostatic enlargement can cause urinary retention, but it would not explain the constipation and blurred vision. Prostatic enlargement primarily affects the urinary system, whereas the other symptoms are more related to anticholinergic effects.

**Option D:** While anticholinergic side effects are the most likely cause, it is not one of the options listed. Therefore, this option is incorrect.

**Clinical Pearl / High-Yield Fact**
When prescribing TCAs, it is essential to monitor patients for anticholinergic side effects, particularly in older adults or those with pre-existing urinary retention or prostatic enlargement. This can help prevent severe complications and improve treatment outcomes.

**✓ Correct Answer: A. Anticholinergic side effects**