Antibiotics: Everything You Should Know

Medically Reviewed by Zilpah Sheikh, MD on March 13, 2024
5 min read

Antibiotics are medicines that help stop infections caused by bacteria. They do this by killing the bacteria or by keeping them from copying themselves or reproducing.

The word antibiotic means “against life.” Any drug that kills germs in your body is technically an antibiotic, but most people use the term when they’re talking about medicine that kills bacteria.

History of antibiotics

Scientists introduced the first antibiotic, salvarsan, in the early 1900s. Since then, antibiotics have changed medicine and added about 23 years to the average human lifespan. Penicillin's discovery in 1928 marked the start of a golden era in finding natural antibiotics, peaking in the 1950s.

Before scientists discovered antibiotics, many people died from minor bacterial infections like strep throat. Surgery was riskier, too. But after antibiotics became available, life expectancy increased, surgeries got safer, and people could survive what used to be deadly infections.

What are antibiotics made of?

Antibiotics are made in nature by soil bacteria and fungi.

You can take antibiotics in a few ways, including:

Antibiotic pills

These can be tablets or capsules, and you'll take them to treat a mild or moderate infection.

Antibiotic injections

This is when you get a shot directly into your blood or muscle. You may need it for a serious infection.

Antibiotic topicals

You put these antibiotics on your skin as a cream, lotion, spray, or drops.

Doctors classify antibiotics into six groups:

Penicillins. You'll take penicillin to treat a range of infections, including those of the skin, chest, and urinary tract.

Cephalosporins. These treat more serious infections such as meningitis.

Aminoglycosides. You'll probably only take these antibiotics in the hospital to treat a serious illness.

Tetracyclines. You'll use these medicines for acne and rosacea

Macrolides. Your doctor may prescribe a macrolide as a substitute for penicillin to treat a lung or chest infection.

Fluoroquinolones. Doctors use these to treat different types of infections.

Broad-spectrum antibiotics

These are antibiotics that work against different types of bacteria.

Narrow-spectrum antibiotics

These focus on a few kinds of bacteria.

Here's a list of antibiotics that your doctor could prescribe:

  • Amoxicillin
  • Amoxicillin/clavulanate
  • Azithromycin
  • Erythromycin
  • Cefdinir
  • Ceftazidime/avibactam
  • Cephalexin
  • Ciprofloxacin
  • Clindamycin
  • Doxycycline
  • Levofloxacin
  • Nitrofurantoin 
  • Penicillin
  • Tetracycline
  • Trimethoprim-sulfamethoxazole 

When you take antibiotics, they start working right away. But how long it takes for you to feel better depends on what kind of infection you have and how bad it is. Usually, you'll start feeling better within a few days, but it might take up to 2 weeks for some infections. Even if you start feeling better before you finish all your medicine, it's important to keep taking it until it's all gone. This helps make sure all the bacteria are killed off so you don't get sick again.




Most bacteria that live in your body are harmless, and some are even helpful. Still, bacteria can infect almost any organ. Fortunately, antibiotics can usually help.

Antibiotics for infection

These are the types of infections that can be treated with antibiotics:

When should you not use antibiotics?

Only bacterial infections can be killed with antibiotics. The common cold, flu, most coughs, some bronchitis infections, most sore throats, and the stomach flu are all caused by viruses. Antibiotics won’t work to treat them. Your doctor will tell you either to wait these illnesses out or prescribe antiviral drugs to help you get rid of them.

It’s not always obvious whether an infection is viral or bacterial. Sometimes, your doctor will do tests before deciding which treatment you need.

Since your gut is full of good and bad bacteria, antibiotics often affect your digestive system while treating an infection. Common side effects include:

Occasionally, you may have other symptoms, like:

These symptoms can mean you’re allergic to your antibiotic, so if you have them, let your doctor know right away.

How long does nausea from antibiotics last?

You may feel sick to your stomach for the entire course of your treatment.

Do antibiotics make you tired?

Unusual tiredness and weakness can be a side effect of some antibiotics, including amoxicillin, azithromycin, and ciprofloxacin.

Antibiotics and alcohol

Some antibiotics can interact with alcohol, so it's best to avoid drinking while taking them and for 48 hours after stopping treatment. 


If you’re taking birth control pills, antibiotics may keep them from working as well as they should, so speak to your doctor about whether alternative birth control methods might be a good idea. Women can also get vaginal yeast infections while taking antibiotics. The symptoms include itching, burning, a vaginal discharge (looks similar to cottage cheese) and pain during sex. It's treated with an antifungal cream.

Antibiotics are powerful germ-fighting tools when used carefully and safely. But up to half of all antibiotic use isn’t necessary. Overuse has led to antibacterial resistance. Bacteria adapt over time and become “super bacteria” or “superbugs.” They change so that antibiotics no longer work on them. They pose a big threat because there aren’t any medicines to kill them.

The best way to help slow the spread of super bacteria is by being smart with antibiotics. Here’s how:

  • Trust your doctor if they say you don’t need them.
  • Don’t take them for a viral infection.
  • Only take the ones your doctor has prescribed for you.
  • Take them as directed.
  • Don’t skip doses.
  • Take them for the full number of days your doctor prescribes.
  • Don’t save them for later.

Antibiotics help fight bacterial infections by killing bacteria or stopping them from multiplying. They've been around since the early 1900s, making surgeries safer and increasing life expectancy. They work well against bacterial infections like strep throat but don't do anything for viral infections like the flu. Using antibiotics too much or when they're not needed can make bacteria resistant to them, making infections more challenging to treat. So, it's important to use antibiotics only when necessary and follow your doctor's instructions carefully.