**Core Concept**
Osteoporosis is a condition characterized by decreased bone density and increased bone resorption, leading to an increased risk of fractures. Treatment options for osteoporosis aim to either increase bone formation or decrease bone resorption. In this context, medications that decrease bone resorption are known as antiresorptives.

**Why the Correct Answer is Right**
Teriparatide is a recombinant form of parathyroid hormone (PTH), which acts as an anabolic agent to increase bone formation. Unlike antiresorptives that decrease bone resorption, teriparatide stimulates osteoblasts to produce new bone matrix, thereby increasing bone density. This anabolic effect of teriparatide is distinct from the antiresorptive effects of other medications used in osteoporosis treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** Alendronate is a bisphosphonate that acts by inhibiting osteoclast-mediated bone resorption, thereby decreasing bone resorption and increasing bone density.
**Option B:** Etidronate is also a bisphosphonate that inhibits bone resorption by preventing the activation of osteoclasts, making it another antiresorptive agent.
**Option C:** Strontium ranelate has both antiresorptive and anabolic effects on bone, although its antiresorptive effects are more pronounced. It decreases bone resorption and increases bone formation, making it distinct from teriparatide.

**Clinical Pearl / High-Yield Fact**
When choosing a medication for osteoporosis, it's essential to consider the patient's risk factors, disease severity, and potential side effects. Antiresorptives like bisphosphonates are often used as first-line treatment, but anabolic agents like teriparatide may be preferred in patients with severe osteoporosis or those who have failed antiresorptive therapy.

**Correct Answer:**
✓ Correct Answer: D. Teriparatide