What Antibiotics Do—and Don’t—Do

Antibiotics have transformed modern medicine, saving millions of lives by treating bacterial infections that were once deadly. Yet they remain one of the most misunderstood medications. Every year, countless people take antibiotics when they won't help—or stop taking them too early when they should continue.

Understanding what antibiotics can and cannot do is one of the best ways to protect your health.

What Antibiotics Do

Antibiotics are medicines that kill bacteria or stop them from multiplying. They are effective against bacterial infections such as:

• Strep throat

• Urinary tract infections (UTIs)

• Bacterial pneumonia

• Cellulitis (skin infections)

• Certain sexually transmitted infections

• Some ear and sinus infections caused by bacteria

When prescribed appropriately, antibiotics can shorten illness, prevent complications, and even save lives.

What Antibiotics Don't Do

Antibiotics do not work against viruses.

That means they won't treat:

• The common cold

• Influenza (flu)

• COVID-19

• Most sore throats

• Most cases of acute bronchitis

• Many sinus infections in their early stages

Taking antibiotics for viral illnesses won't help you recover faster and may expose you to unnecessary side effects.

Why Taking Antibiotics Unnecessarily Is a Problem

Every unnecessary course of antibiotics gives bacteria another opportunity to adapt and become resistant.

This is called antibiotic resistance.

When bacteria become resistant, infections become much harder to treat. Some may require stronger medications, hospital treatment, or intravenous antibiotics. Antibiotic resistance is now considered one of the world's biggest public health threats.

Common Side Effects

Even when antibiotics are needed, they can cause side effects, including:

• Diarrhoea

• Nausea

• Skin rashes

• Thrush (yeast infections)

• Allergic reactions

Some antibiotics can also interact with other medications or affect the effectiveness of oral contraceptive pills in specific situations. Always tell your healthcare provider about every medication and supplement you take.

Should You Always Finish the Course?

The advice has become more nuanced than many people realise.

The most important rule is:

Take antibiotics exactly as prescribed by your healthcare professional.

For many infections, completing the prescribed course is still essential. However, modern guidelines for some conditions recommend shorter courses than were traditionally used. Never stop antibiotics early or keep leftover tablets for future illnesses unless your doctor specifically advises you to do so.

When Should You See a Doctor?

Seek medical advice if:

• Symptoms are severe or worsening

• You have a high fever lasting several days

• You have difficulty breathing

• Symptoms return after initially improving

• You think you may have a bacterial infection

Your clinician can determine whether antibiotics are likely to help or whether another treatment is more appropriate.

The Bottom Line

Antibiotics are powerful medicines—but only when they're used for the right reasons. They are designed to fight bacteria, not viruses. Using them wisely helps protect both your own health and the effectiveness of these life-saving medicines for future generations.

Take-home message: Don't ask whether you need an antibiotic—ask whether your illness is likely to be bacterial.

For more medical content, do check out our Askadoc Youtube.

Stay healthy,

Dr. Joanna