Antibiotics are not effective against viruses because viruses have a completely different structure and replication mechanism compared to bacteria, which antibiotics target. Antibiotics work by attacking specific bacterial structures such as cell walls or protein production machinery—structures that viruses do not possess. Viruses replicate by inserting their genetic material into human cells and using the host's cellular machinery to reproduce, so antibiotics have no target in viruses to attack or inhibit. Therefore, antibiotics cannot kill viruses or stop their replication.
Additionally, using antibiotics for viral infections is ineffective and can lead to harmful side effects and antibiotic resistance, which occurs when bacteria evolve to resist antibiotics. This resistance creates "superbugs" that are harder to treat. Instead, viral infections usually rely on the body's immune system to fight them off, and antiviral medications or vaccines are used specifically to target viruses.