The reason for "drug induced poisoning" is:

We begin by recalling that enzymes possess not only the catalytic or active site, where the normal substrate binds, but also one or more distinct regions called allosteric sites. A molecule that settles itself at an allosteric site is called an allosteric inhibitor. The moment such a molecule occupies the allosteric pocket, it produces a conformational twist in the entire protein. Because protein structure and function are inseparable, this structural alteration finally reaches the catalytic pocket and distorts it so badly that the natural substrate can no longer fit or react.

Now, when a drug behaves as an allosteric inhibitor, the biochemical pathway that depends on that particular enzyme is abruptly blocked. Accumulation of the metabolic intermediate before the blocked step and scarcity of the product after that step together upset the physiological balance. This sudden imbalance is what we refer to in medicinal chemistry as “drug-induced poisoning.”

Let us contrast this with the other possibilities listed in the options. If the drug binds reversibly at the active site (competitive inhibition), the inhibition can usually be overcome by increasing the substrate concentration, so true poisoning does not set in. If the drug brings a minor conformational change exactly at the binding site (option D), the effect is again generally reversible. If the drug binds irreversibly at the active site (option A), it certainly inactivates the enzyme, but such irreversible covalent modification is usually classified as enzyme inactivation or suicide inhibition, not as the specific textbook case of “drug-induced poisoning” asked here.

Hence for “drug-induced poisoning,” the decisive event is

Drug + Enzyme (allosteric site) $$\longrightarrow$$ Drug-Enzyme complex (non-competitive inhibition)

and that description matches the option that says “binding at the allosteric sites of the enzyme.”

Hence, the correct answer is Option B.