Making Sense of Medication Side Effects

Side Effects vs. Allergic Reactions to Medication

Medications are designed to target a specific process in the body, but they can't limit their effects to that one target. For example, NSAIDS, such as ibuprofen, reduce pain and swelling by blocking prostaglandin production, the chemical process that drives inflammation. But prostaglandins also maintain the protective lining of the stomach, so blocking them can lead to stomach irritation, nausea, or even ulcers over time. If your stomach is upset after taking ibuprofen for a headache, that's not a sign that something has gone wrong but rather a predictable consequence of how the drug works.

Side effects of medications tend to be dose-dependent: a higher dose increases both the likelihood and the intensity of the side effects. They're also shaped by individual factors like age, sex, kidney and liver function, other medications or supplements you're taking, and how the drug enters the body (a pill versus an injection versus a topical cream, for example). Side effects can appear when you start a new medication, but they can also show up when you stop one or change your dose. They are also far more common than drug allergies. According to the American Academy of Allergy, Asthma & Immunology, more than 90 percent of unwanted medication reactions are side effects, not allergic responses.¹

When you have an allergic reaction to a drug, your immune system identifies the medication as a harmful foreign substance and mounts an inflammatory response to fight it off. If you have an allergy to pollen or pet dander, your body mounts the same type of immune response. Unlike side effects, allergic reactions are not predictable from the drug's mechanism and are not dose-dependent. A tiny amount of the medication can trigger a full immune response after the first dose. However, an allergic reaction can also develop after you've taken a medication multiple times without any problems, because the immune system can build sensitivity to a drug over repeated exposures. Allergic reactions range from mild to life-threatening, and common symptoms include hives, rash, itching, wheezing, difficulty breathing, and swelling of the lips and tongue.

Side effects and allergic reactions call for different responses. A side effect may be manageable through a dose adjustment or supportive care, and you can often continue taking the medication. If you have an allergic reaction to a drug, you must stop the medication and avoid taking it in the future. If you think you're having an allergic reaction, even a mild one like hives or itching, contact your doctor before taking another dose.

How to Evaluate a Side Effect

Certain reactions to medication are medical emergencies. If you experience any of the following symptoms after taking a medication, go to the nearest emergency room or call 911 immediately:

• Difficulty breathing or wheezing
• Swelling of the face, lips, tongue, or throat
• Loss of consciousness or fainting
• A blistering or peeling rash, especially with fever or mouth sores
• Symptoms that are getting worse with each passing minute

Anaphylaxis, the most severe form of allergic reaction, can become life-threatening within minutes. Do not wait to see if things improve on their own.

Outside of those clear emergencies, it can be difficult to know what to do with a side effect. Do you tolerate it and wait for it to pass? Call your doctor? How do you tell the difference between a normal adjustment and something that needs attention? A few factors can help you evaluate what to do next.

Adjusting to New Medications

When you start a new medication, your body needs time to recalibrate around a new chemical compound. The drug's concentration in your blood builds over the first several doses until it reaches a steady state, and your receptors and enzyme systems adapt to its sustained presence. During that window, side effects are more common. The most frequent side effects caused by medications include stomach upset, loose stools, headaches, drowsiness, dizziness, and mild skin irritation. Most of these begin within the first few days and subside within two to four weeks.

The adjustment period timeline varies by drug. Some medications reach steady state within days, while others can take several weeks. Your prescriber can tell you which side effects are most likely with your specific medication and how long they typically last. In many cases, your prescriber will give you that heads up when writing the prescription. For example, if your doctor starts you on a statin for cholesterol, they'll likely let you know that mild muscle soreness during the first few weeks is common and typically fades. If your prescriber doesn't mention potential side effects, don't be afraid to ask. When you know what side effects to expect and how long they should last, you have a baseline for recognizing when something falls outside the normal adjustment window.

Evaluating Your Side Effects

Three factors can help you assess whether a side effect is something to monitor at home or something to bring to your provider.

Severity and Functional Impact

A side effect that's noticeable but easy to tolerate, like mild drowsiness in the first few days of an antihistamine, is different from one that interferes with your ability to work, drive, or move around your home.

Clinical severity is defined by how a side effect impacts your daily function:

• Mild: You're aware of the symptom, but it doesn't change your routine. Dry mouth during the first week of a new antihistamine, for example, is noticeable but generally not disruptive.
• Moderate: The symptom disrupts your usual activities. Nausea from an antibiotic may keep you from eating regular meals, but your provider can often address this by adjusting when you take the medication or recommending that you take it with food.
• Severe: The symptom prevents you from working, sleeping, eating, or carrying out your daily routine. If a new medication causes persistent vomiting that prevents you from staying hydrated or getting through your day, call your provider rather than waiting to see if it resolves on its own.

A side effect doesn't have to be medically dangerous to warrant a call to your provider. If a side effect is moderate or severe, contact your provider.

Trajectory

Track whether the symptom is improving, holding steady, or getting worse, and use the first few weeks as your benchmark. A side effect that's fading over that window is following the expected adjustment pattern. For example, if a new blood pressure medication causes dizziness that's less noticeable in week three than it was in week one, your body is adjusting to the lower baseline the way it should.

A side effect that's stable or intensifying by the three-to-four-week mark has moved past the normal adjustment window. That doesn't mean the medication is wrong for you, but it does mean your provider needs to know so they can determine the next step.

Onset

Sudden, severe symptoms appearing within minutes of a dose are a red flag and may indicate an allergic reaction rather than a side effect. But onset alone isn't a reliable indicator. Drowsiness after taking a sedating medication or nausea shortly after swallowing a pill are both common and expected. Onset matters most when a severe symptom appears within minutes of a dose, which may signal an allergic reaction, or when a mild side effect escalates fast, like nausea on day one turning into constant vomiting by day two. Both warrant prompt medical attention.

New symptoms can also appear after you've been on a medication for weeks or months, not only when you first start one. If a new symptom appears after you've been stable on a medication for weeks or months, contact your provider. A late-arriving symptom falls outside the normal adjustment window, and your provider can help determine whether or not it's related to the medication.

What to Do When You are Experiencing Side Effects from Medication

If you are experiencing side effects from a new medication, start by keeping track of your symptoms. You don't need a formal log or a special app -- a note on your phone works fine. Take note of what the symptom is, when it started, how intense it feels, and how long it lasts. If you develop a rash or any visible reaction, take a photo. These details are easy to forget once you're sitting in an exam room, and most of us have had the experience of telling a provider, "It's been uncomfortable," without being able to say much more than that. The more specific information you can bring, the easier it is for your provider to identify the cause, decide whether the side effect is expected for your medication, and adjust your treatment if needed.

If you're unsure whether a side effect warrants a visit, reach out to your pharmacist or send a message to your primary care or urgent care doctor through your patient portal. Pharmacists can tell you whether what you're experiencing is a recognized effect of the drug, and they can often suggest ways to manage mild symptoms like nausea or drowsiness at home. And your patient portal is a low-barrier way to describe what's going on and get guidance on whether you need to come in or can continue to monitor.

If you are experiencing side effects, even if they're moderate or severe, don't stop taking your medication without talking to your prescriber. Some medications, including certain blood pressure drugs, antidepressants, and corticosteroids, can cause withdrawal symptoms when discontinued abruptly. In some cases, those withdrawal effects are worse than the side effects that prompted the change. If a side effect is interfering with your daily life or getting worse over time, call your provider. They can taper the dose, adjust the timing, switch you to a different formulation, or move you to another medication in the same class.

Your primary care provider can review what you're experiencing, adjust your dose, change the timing of your medication, or switch you to a different option. Your primary care provider can review what you're experiencing, adjust your dose, change the timing of your medication, or switch you to a different option. MedHelp's on-site pharmacy is also a resource when you have questions about a new symptom and want to know whether it's expected or worth a closer look.

If a side effect is disrupting your daily life and you can't wait for a scheduled appointment, MedHelp's urgent care locations are open seven days a week across the Birmingham metro area.

References

¹American Academy of Allergy, Asthma & Immunology. "Medications and Drug Allergic Reactions." https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/medications-and-drug-allergic-reactions