Antibiotics: What You Need to Know
Antibiotics are powerful and important medications — but only when used correctly. Learn what they treat, why finishing the full course matters, and how to protect yourself and your community from antibiotic resistance.
What Antibiotics Treat — and What They Don't
Antibiotics are medications that kill or inhibit the growth of bacteria. They are effective for bacterial infections such as strep throat, urinary tract infections (UTIs), certain ear infections, skin infections, and pneumonia caused by bacteria.
They have no effect on viruses, which cause the vast majority of respiratory illnesses in Canada, including:
- The common cold
- Influenza (flu)
- COVID-19
- Most sore throats and coughs
- Most cases of bronchitis in otherwise healthy adults
If you are uncertain whether your infection is bacterial or viral, your doctor or pharmacist can help you understand your symptoms and whether a test or prescription is appropriate.
Why Completing the Full Course Matters
One of the most important things you can do when prescribed an antibiotic is finish the entire course — even if you feel better before it is done. Here is why:
- Feeling better does not mean all bacteria have been eliminated — just that their numbers are reduced.
- Surviving bacteria, especially the more resistant ones, can multiply and cause a relapse.
- Incomplete courses are a key driver of antibiotic resistance.
- A second infection may require stronger antibiotics or longer treatment.
There are rare situations where stopping early is appropriate — for example, if your doctor confirms the antibiotic is not needed after test results return. Always follow your healthcare provider's specific instructions.
Antibiotic Resistance: A Growing Concern in Canada
Antibiotic resistance occurs when bacteria evolve to survive antibiotic treatment. The Public Health Agency of Canada identifies antimicrobial resistance as one of the most significant global health threats. Resistant infections are harder to treat, can cause longer illnesses, and in serious cases, can be life-threatening.
Every person who takes an antibiotic unnecessarily or incompletely contributes to this problem. You can help by:
- Only taking antibiotics when prescribed by a healthcare provider.
- Never sharing antibiotics with others or using a leftover prescription.
- Returning unused antibiotics to a pharmacy for safe disposal through Ontario's Take It Back program.
- Getting recommended vaccines, which prevent bacterial infections and reduce the need for antibiotics.
Common Side Effects and Supporting Gut Health
Because antibiotics kill bacteria broadly — not just the harmful ones — they can disrupt the normal bacteria in your digestive system. Common side effects include:
- Nausea, stomach upset, or diarrhea — take most antibiotics with food unless instructed otherwise.
- Vaginal yeast infections in women (due to disruption of normal flora).
- Allergic reactions — rash, hives, or in rare cases, anaphylaxis. Tell your pharmacist about any past antibiotic allergies.
- C. difficile (C. diff) colitis in rare cases, especially with broad-spectrum antibiotics.
Taking a probiotic supplement containing Lactobacillus rhamnosus GG or Saccharomyces boulardii can help reduce antibiotic-associated diarrhea. Take the probiotic at least two hours apart from your antibiotic dose. Ask your pharmacist at Longfields for a specific product recommendation.
Frequently Asked Questions
Why won't my doctor prescribe antibiotics for my cold or flu?
Colds, flu, and most sore throats are caused by viruses. Antibiotics only kill bacteria — they have no effect on viral infections. Taking antibiotics when they are not needed contributes to antibiotic resistance, kills the beneficial bacteria in your gut, and exposes you to unnecessary side effects. Rest, fluids, and over-the-counter symptom relief are the appropriate treatment for most viral illnesses.
What happens if I feel better and stop taking my antibiotic early?
Stopping early is one of the main contributors to antibiotic resistance. When you feel better, it usually means the bacterial population in your body has been reduced — but not necessarily eliminated. The surviving bacteria are often the more resistant ones. If you stop too soon, they can multiply, leading to a relapse that may be harder to treat. Always complete the full prescribed course unless your doctor advises otherwise.
Should I take a probiotic while I'm on antibiotics?
There is good evidence that taking a probiotic alongside antibiotics can help reduce antibiotic-associated diarrhea. Look for products containing Lactobacillus rhamnosus GG or Saccharomyces boulardii, which have the most evidence. Take the probiotic a few hours apart from your antibiotic dose so the antibiotic does not immediately destroy the probiotic bacteria. Ask your pharmacist for a recommendation.
Can I save leftover antibiotics for the next time I get sick?
No. Leftover antibiotics should never be saved or shared. Different bacterial infections require different antibiotics, and using the wrong one — or an incomplete course — can make things worse and contribute to resistance. Bring unused medications to your pharmacy for safe disposal through the Take It Back program available across Ontario.