Understanding Side Effects of Biologics: What’s Common, What’s Rare, and When to Call Your Doctor
Starting a biologic medication can feel like a big step. You may be hopeful about symptom relief and, at the same time, a little nervous about possible side effects. That’s completely normal.
The good news is that biologics have helped millions of people manage autoimmune and inflammatory conditions safely and effectively. Most patients tolerate these therapies well, and care teams closely monitor for side effects throughout treatment.
This guide will walk you through what’s common, what’s less common, and when it’s important to reach out to your healthcare team so that you can feel informed, prepared, and supported.
What to Know
- Biologics are targeted medications that work on specific parts of the immune system
- Most side effects are mild and manageable
- Serious side effects are uncommon and monitored carefully
- Your care team watches for changes through labs, check-ins, and follow-up visits
- You should always feel comfortable reporting new or concerning symptoms
Why Biologics Can Cause Side Effects
Biologics work by calming parts of the immune system that are overactive. Because the immune system also helps protect you from infections, adjusting its activity can sometimes lead to temporary or mild changes in how your body feels.
Everyone responds differently, and many people experience little to no side effects.
Common Side Effects (Usually Mild)
These are the most frequently reported effects and often improve as your body adjusts:
Injection or Infusion Site Reactions
- Redness, swelling, itching, or tenderness
- Typically mild and short-lived
Fatigue
- Feeling more tired than usual for a day or two after treatment
Headache
- Often mild and responsive to hydration or over-the-counter pain relief (if approved by your doctor)
Cold-Like Symptoms
- Runny nose, mild sore throat, or congestion
Upset Stomach
- Nausea or mild abdominal discomfort
These symptoms are usually not dangerous and can often be managed with simple comfort measures. However, let your care team know if they persist or interfere with daily life.
Less Common but Important to Watch For
Biologics can slightly increase your risk of infections because they affect immune activity. Your care team monitors for this carefully.
Contact your provider if you notice:
- Fever or chills
- Persistent cough
- Shortness of breath
- Burning with urination
- Unusual fatigue that doesn’t improve
Other less common effects may include:
- Skin rashes
- Changes in liver enzymes or blood counts (found on routine labs)
- Joint or muscle aches
Most of these are identified early through regular monitoring.
Rare Side Effects
Serious side effects are uncommon, but your care team stays vigilant. These may include severe allergic reactions, serious infections, or certain blood or immune-related changes.
To help reduce these risks, before starting therapy your provider reviews your health history, performs screening tests, and determines whether a biologic is appropriate for you.
How Your Care Team Monitors Safety
Your biologic treatment plan is guided and monitored by your care team from start to finish. Monitoring may include:
- Baseline blood tests before starting
- Periodic lab work during treatment
- Screening for infections such as tuberculosis or hepatitis
- Observation during and after infusions or injections
- Regular follow-up appointments
When to Call Your Doctor About Biologic Side Effects
Call your care team if you experience:
- Fever over 100.4°F (38°C)
- Signs of infection
- Chest pain or trouble breathing
- Severe rash or swelling
- New or worsening symptoms that concern you
Remember, if something doesn’t feel right, don’t minimize your symptoms; instead, consult with your doctor, even if you’re unsure.
Practical Tips for Communicating with Your Care Team
- Keep a simple symptom journal
- Note when symptoms start and how long they last
- Bring questions to appointments
- Be honest about how you’re feeling
Open communication helps your care team understand what you’re experiencing and make adjustments when needed. Remember, you’re not just a bystander, you’re the most important partner in your care.
Moving Forward Confidently with Biologics
Most people who use biologics experience few or mild side effects, and serious problems are uncommon. With thoughtful screening, ongoing monitoring, and open communication, biologic treatment can be both safe and highly effective.
As you move forward, know that your care team is there to guide you, answer your questions, and adjust your treatment if needed. With their support, you can move forward confidently with biologics and focus on living your life more fully.
Frequently Asked Questions
Do all biologics have the same side effects?
No. Each medication works slightly differently, so side-effect profiles vary. Your provider can explain what’s most relevant to your specific treatment.
Will side effects go away over time?
Many mild side effects improve as your body adjusts during the first few weeks or months.
Can I still get vaccines while on biologics?
Some vaccines are safe and recommended, while others may need to be avoided. Always check with your provider first.
Should I stop my biologic if I feel unwell?
Never stop medication without medical guidance. Call your care team so they can review your symptoms and adjust your treatment safely.
How often will I need monitoring?
Monitoring schedules vary, but most patients have regular labs and follow-ups throughout treatment.