It takes a pharmacist years of education and training to learn the different classes and medications and their MOAs — mechanisms of action— to assume, memorize, or wing it—is dangerous. Memorizing does not work because different drug classes work/don’t work with and interact with disease states, drugs, allergies, environments, and food. The only way to know how a particular drug affects any or all of these factors is knowing how the drug works on the body at the systemic and cellular if not atomic level and to do that you must know and understand its mechanism of action.
From there you can understand the class and defer the knowledge to the class with... caveats to the particular drug in question.
That’s why pharmacists have such extensive chemical, therapeutic, and biochemical knowledge.
It’s also why we’re called the GATEKEEPERS.