**Core Concept**
Norplant 1 is a contraceptive implant consisting of six small rods made of levonorgestrel, a progestin. It works by releasing a steady amount of this hormone into the bloodstream, which in turn prevents ovulation and fertilization. The effectiveness of Norplant 1 is influenced by its ability to maintain a certain level of levonorgestrel in the body, which is affected by the duration of use.

**Why the Correct Answer is Right**
The correct answer is based on the pharmacokinetics of levonorgestrel, which is the active ingredient in Norplant 1. Levonorgestrel is metabolized by the liver enzyme CYP3A4, and its half-life is approximately 24-48 hours. Studies have shown that the contraceptive efficacy of Norplant 1 is maintained for up to 5 years, as long as the levonorgestrel levels remain above a certain threshold. This is because ovulation suppression is the primary mechanism of action of progestin-only contraceptives like Norplant 1.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a specific duration of time for the effectiveness of Norplant 1.
**Option B:** This option is incorrect because it suggests a shorter duration of effectiveness than what has been established in clinical trials.
**Option C:** This option is incorrect because it implies that Norplant 1 is effective for a longer period than its actual duration.

**Clinical Pearl / High-Yield Fact**
One key point to remember is that the effectiveness of Norplant 1 is influenced by the individual's body weight, as well as their metabolism of levonorgestrel. Therefore, it's essential to consider these factors when counseling patients about the use of this contraceptive method.

**Correct Answer:** C. 5 years