Adverse Reactions vs Side Effects: Are They the Same Thing?

When taking medication, you might hear the terms adverse reactions and side effects used to describe unwanted outcomes. While these phrases are sometimes used interchangeably, they actually refer to different concepts in medicine. Understanding the distinction can help patients and caregivers better recognize, report, and manage medication-related issues.

What Is a Side Effect?

A side effect is an unintended effect of a medication that occurs in addition to its intended therapeutic action. These effects are generally predictable and are often identified during clinical trials before a drug is approved for use.

Side effects can be beneficial, neutral, or harmful. For example, diphenhydramine (a common allergy medication) can cause drowsiness as a side effect. For this reason, it is sometimes used to help with short-term sleep problems.

Side effects can range from mild to bothersome, but are typically not dangerous. Examples include headaches, nausea, drowsiness, or mild skin rashes. Healthcare professionals often inform patients about possible side effects so they know what to expect and when to seek help if needed.

What Is an Adverse Reaction?

An adverse reaction—also called an adverse drug reaction (ADR)—is a harmful or unpleasant response to a medication that is unintended and can occur even when the drug is used correctly. Adverse reactions are often more serious than common side effects and may require medical intervention, changes in dosage, or discontinuation of the drug. They can be predictable (dose-related) or unpredictable (such as allergic reactions or unique patient susceptibilities).

According to the World Health Organization, an adverse drug reaction is "a response to a drug product that is harmful and unintended," and these reactions are a leading cause of hospital admissions and increased healthcare costs in some countries. Examples include Stevens-Johnson syndrome from terbinafine and blood clots from certain oral contraceptives.

Key Differences Between Adverse Reactions and Side Effects

Overlap and Misconceptions

The terms are sometimes used interchangeably, and even regulatory agencies may refer to side effects as "adverse reactions." For instance, the FDA uses both terms to describe unwanted effects related to drug use. However, in clinical practice and pharmacovigilance, distinguishing between the two is important. Side effects are generally expected and less concerning, while adverse reactions are unexpected and may pose significant health risks.

Recognizing the difference helps patients and healthcare providers:

• Know which symptoms are normal and which are cause for concern
• Report serious events promptly for better drug safety monitoring
• Make informed decisions about continuing or stopping a medication

For example, mild stomach upset may be a side effect and not require stopping the medication, while symptoms like difficulty breathing or severe rash could signal an adverse reaction and need immediate medical attention.

How to Reports Side Effects or ADRs

Experiencing an unexpected side effect from a medication or vaccine can be concerning. Reporting these events is key in ensuring the ongoing safety of medical products for everyone. Your healthcare provider can serve as a great resource, and should always be informed of any side effects you experience.

In the United States, there are two primary channels for reporting side effects: the U.S. Food and Drug Administration (FDA) and to the product's manufacturer. The FDA is the primary government agency responsible for monitoring the safety of drugs, vaccines, medical devices, and other products. They have specific programs for collecting and analyzing reports of adverse events.

Reporting to the Manufacturer

There are a few different ways to find manufacturer contact information:

• Product Labeling: The medication's package insert or patient information leaflet will typically include the manufacturer's name and contact information.
• Manufacturer's Website: The "Contact Us" or "Medical Information" section of the manufacturer's website will provide phone numbers or online forms for reporting adverse events. For example, major pharmaceutical companies like Pfizer and Teva have dedicated sections on their websites for this purpose.
• Your Pharmacist: Your pharmacist can also be a valuable resource for finding the manufacturer's contact information.

Reporting to MedWatch

The FDA's MedWatch program is for reporting serious adverse events, product quality problems, and product use errors for human medical products, including:

• Prescription and over-the-counter medications
• Biologics (such as blood products and cell and gene therapies)
• Medical devices
• Special nutritional products (such as dietary supplements and infant formulas)
• Cosmetics

There are several ways for consumers and healthcare professionals to submit a report:

• Online: The preferred method is to use the MedWatch Online Voluntary Reporting Form (Form FDA 3500B for consumers and 3500 for healthcare professionals). The online form is designed to be user-friendly and can be accessed on the FDA's website.
• Phone: You can report a side effect by calling the FDA at 1-800-FDA-1088.
• Mail or Fax: You can download the appropriate form from the FDA website, complete it, and either mail it to the address provided on the form or fax it to 1-800-FDA-0178.

Vaccine Adverse Event Reporting System (VAERS)

For side effects related to vaccines, the appropriate channel is the Vaccine Adverse Event Reporting System (VAERS). This is a national vaccine safety surveillance program co-managed by the FDA and the Centers for Disease Control and Prevention (CDC).

How to Report to VAERS:

• Online: The preferred and easiest method is to submit a report through the secure VAERS online reporting system.
• Phone: You can call the VAERS toll-free information line at 1-800-822-7967 for assistance or to have a form mailed to you.
• Mail: You can download a writable PDF form from the VAERS website and mail it to the address provided.

Conclusion

While both side effects and adverse reactions refer to unwanted effects of medications, side effects are generally predictable and manageable, whereas adverse reactions are harmful, potentially severe, and may require urgent intervention. Knowing the distinction empowers patients to use medications safely and seek help when necessary.

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