**Core Concept**
Exenatide is a medication used to treat diabetes mellitus by mimicking the action of incretin hormones. It belongs to the class of glucagon-like peptide-1 (GLP-1) analogues, which help regulate blood sugar levels by enhancing insulin secretion and suppressing glucagon release. Exenatide is primarily used in the management of type 2 diabetes mellitus, not type 1 diabetes mellitus.

**Why the Correct Answer is Right**
Exenatide works by binding to the GLP-1 receptor, which is present on the surface of pancreatic beta cells. This binding stimulates insulin secretion in a glucose-dependent manner, meaning that insulin is released only when glucose levels are elevated. Simultaneously, exenatide suppresses glucagon secretion, which is the hormone responsible for raising blood glucose levels. However, type 1 diabetes mellitus is characterized by the autoimmune destruction of pancreatic beta cells, making it impossible for exenatide to stimulate insulin secretion. Therefore, exenatide is not used in the treatment of type 1 diabetes mellitus.

**Why Each Wrong Option is Incorrect**
**Option A:** Decreases glucagon secretion - This statement is true. Exenatide suppresses glucagon secretion, which is a key mechanism by which it helps regulate blood sugar levels.
**Option B:** It is GLP 1 analogue - This statement is also true. Exenatide is a synthetic analogue of the incretin hormone GLP-1.
**Option D:** Given subcutaneously - This statement is true as well. Exenatide is administered via subcutaneous injection to facilitate its absorption into the bloodstream.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that GLP-1 analogues like exenatide are not suitable for patients with type 1 diabetes mellitus, as they rely on the presence of functional pancreatic beta cells to stimulate insulin secretion.

**✓ Correct Answer: C. Used in type 1 DM**