## Core Concept
Adulterants in heroin are substances added to the drug to increase its bulk and profitability. These adulterants can be various pharmacologically active or inactive compounds. Common adulterants include fillers like sugars, starches, and other substances.

## Why the Correct Answer is Right
The correct answer, **D. Paracetamol**, is not typically used as an adulterant in heroin. Heroin adulterants are usually substances that can mimic the effects of heroin or simply bulk up the product without causing immediate harm. Paracetamol (acetaminophen) is a common over-the-counter analgesic and antipyretic but is not commonly associated with heroin adulteration.

## Why Each Wrong Option is Incorrect
- **Option A:** *Starch* is a common adulterant used in heroin. It is pharmacologically inactive and can help to bulk up the product.
- **Option B:** *Quinine* can be used as an adulterant. It has a bitter taste, which can somewhat mimic the bitter taste associated with some heroin products, and it has been historically used for this purpose.
- **Option C:** *Lactose* is another substance that can be used to adulterate heroin. Like starch, it is inert and can help increase the volume of the product.

## Clinical Pearl / High-Yield Fact
A key point to remember is that adulterants in illicit drugs like heroin can vary widely and may include substances like *quinine*, *caffeine*, *lidocaine*, and various fillers. The use of these adulterants can lead to a range of health issues, including overdose, allergic reactions, and pharmacological interactions.

## Correct Answer: D. Paracetamol.