Why Do Some Medications Have Side Effects?

Summary

Medication side effects are unwanted effects that can occur when taking a medicine. They may result from how a drug works in the body, how it is processed, the dose taken or interactions with other medications and supplements. Some side effects are mild and temporary, while others require medical attention. Understanding what to expect, recognizing warning signs and speaking with a pharmacist or practitioner can help you manage side effects safely.

What are medication side effects?

A medication side effect is an unintended effect that occurs when you take a medicine as directed. Some side effects are mild, such as nausea or a headache. Others may affect your daily routine or require a change to your treatment.

Side effects vary depending on the medication and the person taking it. One person may experience no noticeable effects, while another may find the same medication causes discomfort.

It's also important to distinguish side effects from allergic reactions. A side effect is an unwanted effect of a medication, while an allergic reaction involves the immune system and can sometimes be serious.

Experiencing a side effect does not automatically mean a medication is unsuitable for you. However, new, persistent or concerning symptoms should be discussed with a healthcare professional.

Why do medications cause side effects?

Medications are designed to produce specific effects in the body, but their actions can sometimes affect other processes, too. Several factors can contribute to side effects.

1. How the medication works

A medication may affect more than one function in the body. Even when it works as intended, those additional effects can cause unwanted symptoms.

For example, some antihistamines can cause drowsiness because of how they affect the nervous system. Some blood pressure medications can cause dizziness as blood pressure changes.

2. The dose you take

The dose can influence both a medication's benefits and its potential side effects. Some effects become more likely or more noticeable at higher doses.

This is one reason practitioners may start with a particular dose and adjust it according to your response. Never change your dose on your own to manage a side effect.

3. How your body processes the medication

Your body absorbs, distributes, breaks down and eliminates medications. Differences in these processes can affect how a drug works and how long it remains in your system.

Age, kidney function, liver function and other health conditions can influence how certain medications are processed.

4. Other medications and supplements

Taking multiple medications can increase the chance of an interaction. One drug may change how another works, increase its effects or raise the risk of side effects.

OTC medicines, vitamins and herbal supplements can also contribute to interactions. Keep an up-to-date list of everything you take and share it with your pharmacist and other practitioners involved in your care.

5. Individual differences

Your medical history, genetics, allergies and sensitivity to particular medications can affect how you respond to treatment.

This helps explain why a medication may work well for one person but cause unwanted effects in another.

What are the most common medication side effects?

The effects you experience depend on the medication. Some commonly reported side effects include:

• Nausea or stomach discomfort: Some medications can irritate the digestive system or affect how your body responds to food.
• Headaches: Headaches may occur with certain medications or when your body adjusts to treatment.
• Dizziness: Some medications affect blood pressure, balance or alertness.
• Drowsiness or fatigue: Certain drugs can affect the central nervous system or contribute to tiredness.
• Changes in bowel habits: Some medications cause constipation or diarrhoea.
• Skin reactions: Rashes or itching can occur with certain medicines and may require assessment.

These symptoms can have many causes, so you should not automatically assume that a medication is responsible. If symptoms begin after starting a new drug or changing a dose, let your pharmacist or practitioner know.

How long do medication side effects last?

There is no single timeline for medication side effects. Some may improve as your body adjusts to a medication, while others can persist for as long as you take it.

How long a side effect lasts depends on factors such as:

• The medication and dose.
• How your body processes the drug.
• Whether the medication is taken regularly.
• Other medications or health conditions.
• The type and severity of the side effect.

Do not assume that a symptom will disappear on its own. If it persists, worsens or interferes with your daily activities, speak with your pharmacist or practitioner.

For blood pressure medications in particular, do not stop treatment simply because you feel better or experience a side effect. Uncontrolled blood pressure can carry serious health risks, and some medications may need to be reduced gradually under professional guidance.

How can you manage medication side effects?

If you think a medication is causing an unwanted effect, there are several steps you can take.

Keep track of your symptoms

Note when the symptom began, how often it occurs and whether it follows a dose. Record any recent changes to your medication, supplements or routine.

This information can help your pharmacist or practitioner assess whether the medication may be contributing to the problem.

Check the medication instructions

Read the patient information provided with your medication. It may explain common side effects, interactions, precautions and when to seek medical attention.

If the instructions are unclear, ask a pharmacist to explain them.

Review your medications with a pharmacist

A pharmacist can review your prescriptions, OTC medicines and supplements to identify potential interactions or other factors that may contribute to your symptoms.

Depending on the situation, they may recommend monitoring your symptoms, adjusting when you take a medication or contacting your prescriber about alternatives.

Ask whether your treatment needs to change

If a side effect is persistent or difficult to manage, your practitioner may consider whether a different dose or medication would be appropriate.

The decision depends on the benefits of your current treatment, the severity of the side effect and your individual health needs.

Do not stop a medication, change your dose or take an additional medicine to counteract a side effect without appropriate guidance.

When should you seek medical attention?

Contact a pharmacist or practitioner if a side effect is persistent, worsening, unexpected or interfering with your daily life. Seek advice promptly if you develop new symptoms after starting a medication or changing your dose.

Some symptoms require emergency attention. These include:

• Difficulty breathing or swelling of the tongue or throat.
• Severe chest pain.
• Fainting or loss of consciousness.
• Sudden weakness, difficulty speaking or other possible signs of a stroke.
• A severe allergic reaction.

Call your local emergency services if you experience these symptoms. Do not wait for a routine appointment or rely on an online symptom checker.

How Pocketpills can help you manage your medications

Understanding your medications can help you feel more prepared to recognize side effects and know when to ask for help.

Pocketpills offers digital healthcare and prescription management services, with access to available support from healthcare practitioners and pharmacists.

If you are experiencing a possible side effect, speak with a pharmacist or your prescribing practitioner before making changes to your treatment. They can help you understand whether the symptom may be medication-related and what steps may be appropriate.

Frequently asked questions

Why do some people experience medication side effects while others do not?

People can respond differently to the same medication because of differences in age, genetics, health conditions, kidney or liver function, dosage and other medications they take.

Do all medications have side effects?

All medications can have potential side effects, but not everyone experiences them. The likelihood and severity depend on the medication and individual circumstances.

Do medication side effects go away?

Some side effects improve over time, while others persist or require a change in treatment. Speak with a pharmacist or practitioner if symptoms continue or become difficult to manage.

What should I do if my blood pressure medication causes side effects?

Contact your pharmacist or prescribing practitioner to discuss your symptoms. They can help determine whether the medication may be responsible and whether monitoring or a treatment adjustment is appropriate. Do not stop taking your medication without professional guidance.

Can taking multiple medications increase side effects?

Yes. Some medications interact and can increase the likelihood or severity of certain side effects. Tell your pharmacist about all prescription medicines, OTC products, vitamins and supplements you take.

How can I tell if a symptom is a side effect or an allergic reaction?

It can be difficult to tell without a clinical assessment. Allergic reactions may involve hives, itching or swelling, and severe reactions can cause difficulty breathing or throat swelling. Seek emergency help for signs of a severe allergic reaction.

Sources

• Health Canada: Drug Product Database
• MedlinePlus: Drug Reactions
• U.S. Food and Drug Administration: Understanding Unintended Interactions
• Heart & Stroke: High Blood Pressure
• Hypertension Canada