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Allergy Medications and Testing: When to Stop and Why
If you or your child are scheduled for allergy testing, your allergist will likely provide specific instructions about temporarily stopping certain medications beforehand. Understanding which medications need to be paused, for how long, and why this preparation is necessary can help ensure your testing provides the most accurate results possible.
Why some medications need to be stopped before allergy testing
Skin prick testing and food challenges work by evaluating your body's immediate allergic response to specific substances. Certain medications, particularly antihistamines, are designed specifically to block this response – that's precisely how they relieve allergy symptoms.
If these medications remain active in your system during testing, they can mask reactions that would otherwise be visible, potentially leading to "false negative" results where allergies go undetected.
Which tests require stopping medications?
Skin prick testing
For skin prick testing, antihistamines must be stopped because they:
- Block the histamine response that creates the wheal and flare reaction
- Prevent accurate measurement of reactions to allergens
- Could lead to missed diagnoses if reactions are suppressed
Food challenges
For food challenges, antihistamines must also be stopped because they:
- Could mask initial mild symptoms of an allergic reaction
- Might allow consumption of larger doses before symptoms appear
- Would interfere with the ability to determine true tolerance
Blood testing
For blood testing (specific IgE testing), no medication adjustments are typically needed because:
- These tests measure antibodies present in the blood
- Antihistamines don't affect the level of existing antibodies
- Results will be accurate regardless of current medication use
This makes blood testing particularly useful for patients who cannot stop their antihistamines for medical reasons.
Specific medication guidelines
Antihistamines
Antihistamines are the primary medications that must be stopped before skin testing and food challenges. The required stopping period depends on the specific medication:
Short-acting antihistamines (stop 48 hours before testing)
- Chlorpheniramine (Piriton)
- Hydroxyzine (Ucerax, Atarax)
- Acrivastine (Benadryl Allergy Relief)
- Diphenhydramine (Nytol, Benadryl Allergy)
Long-acting antihistamines (stop 5 days before testing)
- Cetirizine (Zirtek, Zyrtec)
- Levocetirizine (Xyzal)
- Loratadine (Claritin)
- Desloratadine (Neoclarityn)
- Fexofenadine (Telfast, Allegra)
- Bilastine (Ilaxten)
Medications containing antihistamines
Some medications contain antihistamines even though they are not primarily marketed as allergy treatments:
- Cough and cold preparations: Many children's cough medicines contain antihistamines and should be stopped 48 hours before testing
- Sleep aids: Over-the-counter sleep medications often contain diphenhydramine and should be stopped 48 hours before testing
- Travel sickness medications: These frequently contain antihistamines and should be stopped 48–72 hours before testing
- Some eye drops: Those containing antihistamines should be stopped before testing
Medications that do NOT need to be stopped
Many common medications don't interfere with skin testing and can be continued as usual:
- Corticosteroids: Oral steroids (like prednisolone), inhaled steroids (for asthma), and nasal steroids (for hay fever) do not affect skin testing results
- Leukotriene modifiers: Medications like montelukast (Singulair) and zafirlukast (Accolate) do not need to be stopped
- Asthma medications: Bronchodilators, including both short-acting (e.g., salbutamol/Ventolin) and long-acting (e.g., salmeterol) varieties, do not interfere with testing
- Topical steroid creams: These can be continued, but should not be applied to the specific areas where skin testing will be performed
- Most non-allergy medications: Blood pressure medications, diabetes medications, and most other prescriptions do not affect skin test results
Special considerations for different age groups
Children
For children, special considerations include:
- Check cough medicines carefully: Many paediatric formulations contain antihistamines that parents might not be aware of
- Maintaining other medications: Continue medications for conditions like asthma or eczema, as stopping these could trigger flares
- Timing considerations: For very young children, try to schedule testing at times when they're typically more settled
Adults and older adults
For adults, particularly those taking multiple medications:
- Medication review: Bring a complete list of all medications to discuss with your allergist before testing
- Multiple health conditions: Some adults cannot safely stop certain medications and may need to rely on blood testing instead of skin testing
- Interactions: Some medications may have withdrawal effects if stopped suddenly – always consult with your prescribing doctor if unsure
Practical approaches to stopping medications
Temporarily stopping antihistamines can be challenging, especially during high allergy seasons. Here are some practical approaches:
Managing symptoms during the medication-free period
- Timing your testing: If possible, schedule testing during periods when your allergy symptoms are naturally less severe
- Non-medication strategies: Use saline nasal irrigation, eye compresses, or air filtration to help manage symptoms without medications
- Limited local treatments: For localised symptoms, ask your allergist whether certain topical treatments away from testing sites are permitted
What to do if you cannot stop medications
If you or your child absolutely cannot stop antihistamines due to severe symptoms:
- Discuss with your allergist: They may recommend blood testing as an alternative
- Partial withdrawal: Sometimes stopping for a shorter period is better than not stopping at all
- Modified testing protocols: In some cases, allergists may perform testing with adjusted interpretation criteria
What happens if medications aren't stopped as instructed?
If antihistamines remain in your system during testing:
- Reduced or absent skin reactions: Even when allergies are present, the skin may not react
- Missed diagnoses: Significant allergies could go undetected
- Need for retesting: You may need to return for additional testing, causing delay and inconvenience
If you accidentally take an antihistamine before your scheduled test, it's best to contact your allergist's office promptly to discuss whether rescheduling is necessary.
Common questions about medication withdrawal
"Can I take just one dose of antihistamine if my symptoms are severe?"
Even a single dose of an antihistamine can affect skin test results for 24–72+ hours, depending on the medication. If severe symptoms require treatment, contact your allergist for guidance rather than compromising your test results.
"Do I need to stop my asthma inhaler before testing?"
No. Asthma inhalers (both preventers and relievers) should be continued as prescribed. Stopping these medications could trigger asthma symptoms and does not improve test accuracy.
"What about antihistamine nasal sprays and eye drops?"
Antihistamine nasal sprays (e.g., Azelastine) and eye drops should ideally be stopped before skin testing, especially if testing will be done on the face. However, steroid nasal sprays can usually be continued.
"Can I take painkillers before the test?"
Most common painkillers (e.g., paracetamol, ibuprofen) do not affect skin test results and are generally safe to take. However, check combination cold/flu products carefully, as some may contain antihistamines.
Planning for your allergy testing appointment
To ensure your testing goes smoothly:
- Review medication instructions: Carefully follow the guidance provided by your allergist
- Create a reminder system: Set calendar alerts for when to stop specific medications
- Prepare questions: Note any concerns about stopping medications to discuss with your allergist
- Communicate: If you've taken an antihistamine by mistake, inform the clinic right away
- Bring a medication list: Take a complete list of all medications you or your child regularly take
Following up after testing
Once testing is complete, your allergist will advise when to resume medications. In most cases, antihistamines can be restarted immediately after testing for symptom relief.
If new medications are recommended based on the results, your allergist will explain how they fit with your current treatment plan.
The bigger picture: Getting accurate results
While stopping medications temporarily may be inconvenient, it is vital for accurate testing. Clear identification of your allergens ensures that:
- Avoidance measures target the correct triggers
- Medication plans are tailored to your needs
- Emergency plans reflect actual allergic sensitivities
- Unnecessary lifestyle or dietary restrictions are avoided
By carefully following medication guidance before your appointment, you help your allergist obtain the most useful and accurate information possible for managing allergies effectively.
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