What is the purpose of designer drugs?

These drugs are illicitly produced with the intent of developing substances that differ slightly from controlled substances in their chemical structure while retaining their pharmacological effects.

Explanation:

Recently, the abuse of clandestinely synthesized drugs has re-emerged as a major worldwide problem. These drugs are illicitly produced with the intent of developing substances that differ slightly from controlled substances in their chemical structure while retaining their pharmacological effects. These substances are commonly known as designer drugs and fall under several drug categories. The following section describes these drugs of concern and their associated risks.

answer; (b) i believe its metabolic rate of the patient; plz check first