**Dryness of mouth caused by antipsychotics due to their -**

**Core Concept**
The dryness of mouth caused by antipsychotics is primarily due to their anticholinergic properties. Anticholinergic agents block the action of the neurotransmitter acetylcholine, which plays a crucial role in stimulating salivary gland secretion. This blockade leads to a decrease in salivary flow, resulting in dryness of the mouth.

**Why the Correct Answer is Right**
Antipsychotic medications, particularly the typical antipsychotics, possess significant anticholinergic activity. They inhibit the action of acetylcholine at muscarinic receptors in the salivary gland, leading to a reduction in salivary secretion. This anticholinergic effect is responsible for the dryness of the mouth, which is a common side effect of antipsychotic therapy. The reduction in salivary flow can also contribute to other oral health issues, such as dental caries and xerostomia.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the anticholinergic properties of antipsychotics.
* **Option B:** Although antipsychotics can cause orthostatic hypotension due to their alpha-adrenergic blockade, this is not related to dryness of the mouth.
* **Option C:** This option is not directly related to the mechanism of dryness of the mouth caused by antipsychotics.

**Clinical Pearl / High-Yield Fact**
To remember the anticholinergic side effects of antipsychotics, use the mnemonic "BRIGHT": Blurred vision, Restlessness, Hallucinations, Increased heart rate, Tachycardia, and Glaucoma. This mnemonic can help you recall the common anticholinergic side effects associated with antipsychotic therapy.

**Correct Answer: D. Anticholinergic properties.**