**Core Concept**
The problem in new drug designing arises from the unwanted interactions of the drug with proteins other than the intended target protein. This phenomenon is known as off-target effects or non-specific binding, which can lead to adverse effects, toxicity, and reduced efficacy of the drug. The ideal goal in drug designing is to create a molecule that selectively binds to the target protein with high affinity and specificity.

**Why the Correct Answer is Right**
Increasing drug interaction with non-target proteins (off-target effects) is a significant challenge in new drug designing. This occurs when the drug molecule binds to proteins other than the intended target, leading to unintended consequences such as activation of enzymes, receptors, or channels that can cause adverse effects. For instance, a drug designed to inhibit a particular enzyme might also bind to a related enzyme, leading to inhibition of the latter and causing unintended side effects. The development of drugs with high specificity and affinity for the target protein is crucial to minimize off-target effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Decreasing interaction of drug with target proteins is not a problem in new drug designing, as the goal is to achieve a high affinity between the drug and the target protein.

**Option C:** Decreasing potency of drugs is a concern, but it is not the primary problem in new drug designing. While decreasing potency can be a result of off-target effects, it is not the root cause.

**Option D:** This option is a repeat of Option C and is therefore incorrect for the same reasons.

**Clinical Pearl / High-Yield Fact**
A key consideration in new drug designing is the concept of "selectivity" – the ability of a drug to discriminate between its intended target and other proteins. Drugs with high selectivity are less likely to cause off-target effects and are generally safer and more effective.

**✓ Correct Answer: B. Increasing drug interaction with non-target proteins.**