First, what is a drug? What makes a drug?
A drug is a small molecule that has a binding affinity to its target (this usually is a protein).
What does that mean?
Drugs are specific to their target. The job of the drug is to disable and stop its target from functioning. Essentially, the better the drug and the protein fit with each other, the more effective the drug is!
If the target is a protein, it has an area where the drug joins/connects to it. This area can either be a receptor or a pocket.
This isn’t the only way drugs work. Sometimes, drugs can be ‘dummy’ molecules that are substitutes for real molecules. In such a case, the drug works by standing in place for the molecule, and thus inhibiting the molecule from completing its function. A popular example of this is remdesivir, an adenosine analog. Once the viral RNA polymerase attaches remdesivir to a copied strand of the virus, the virus’s replication cannot continue. Without copying its genes, the virus cannot assemble, grow, and exit the cell, which ultimately prohibits the virus from spreading to other cells.
The way a drug works is called its mechanism of action.