**Core Concept**
The question tests the student's knowledge of the effects of Oral Contraceptive Pills (OCPs) on the female body, specifically the metabolic, vascular, and hormonal changes they induce. OCPs contain **estrogen** and **progestin**, which have various effects on the body.

**Why the Correct Answer is Right**
OCPs are known to have several effects, including changes in **lipid metabolism**, **coagulation factors**, and **blood pressure**. They can increase the risk of **thromboembolic events** due to their effect on **clotting factors** and **fibrinolysis**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because OCPs can cause an increase in **blood pressure**.
**Option B:** Incorrect as OCPs can affect **glucose tolerance**.
**Option C:** Incorrect because OCPs can increase the risk of **thromboembolism**.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that OCPs can have varying effects on different women, and their use requires careful consideration of the individual's medical history and risk factors.

**Correct Answer:** D. Decrease in blood pressure.