Allergy Medications and Testing: When to Stop and Why
In a nutshell
- Antihistamines must be stopped before skin prick testing and food challenges to avoid false negative results
- Short-acting antihistamines (such as chlorphenamine/Piriton) need 48 hours; long-acting ones (cetirizine, loratadine, fexofenadine) need five days
- Antihistamines relieve symptoms for around 24 hours, but they keep suppressing skin test reactions for days after the last dose
- Blood tests (specific IgE) do not require stopping any medication
- Most other medications, including inhalers, nasal steroids, and montelukast, do not need to be paused
- If you accidentally take an antihistamine before your test, contact the clinic straight away
Before skin prick testing or a food challenge, antihistamines must be stopped to prevent false negative results. Short-acting antihistamines such as chlorphenamine require 48 hours; long-acting antihistamines such as cetirizine, loratadine, and fexofenadine require five days. Blood tests (specific IgE) do not require stopping any medication. Inhalers, nasal steroids, and montelukast do not need to be paused before any type of allergy test.
If you or your child are scheduled for allergy testing, your allergist will provide specific instructions about temporarily stopping certain medications beforehand. Understanding which medications need to be paused, for how long, and why this preparation matters helps ensure your testing gives 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 to block exactly that response; that is how they relieve allergy symptoms.
If these medications remain active in your system during testing, they can mask reactions that would otherwise be visible, producing "false negative" results where real allergies go undetected. We explain what false negatives look like in our guide to interpreting your test results.
How long to stop each antihistamine: quick reference
| Medication | Common UK brands | Stop before testing |
|---|---|---|
| Chlorphenamine (chlorpheniramine) | Piriton | 48 hours |
| Hydroxyzine | Atarax, Ucerax | 48 hours |
| Acrivastine | Benadryl Allergy Relief | 48 hours |
| Diphenhydramine | Nytol, Benadryl Allergy (US) | 48 hours |
| Cetirizine | Zirtek, Zyrtec | 5 days |
| Levocetirizine | Xyzal | 5 days |
| Loratadine | Clarityn, Claritin | 5 days |
| Desloratadine | Neoclarityn | 5 days |
| Fexofenadine | Telfast, Allegra | 5 days |
| Bilastine | Ilaxten | 5 days |
These are the timings we use at the clinic. If you have been given different instructions for a specific test, follow the instructions on your appointment letter.
How long do antihistamines stay in your system?
The symptom relief from a modern antihistamine lasts around 24 hours, which is why most are taken once daily. But the effect on your skin's ability to react lasts considerably longer than the effect you feel. After the last dose of a long-acting antihistamine such as cetirizine or fexofenadine, skin test reactivity can remain suppressed for several days while the medication clears from the tissues.
That gap between "symptoms back" and "skin reacting normally" is why the stopping period is five days rather than one, and why even a single dose in the days before your appointment can affect the result. Older sedating antihistamines such as chlorphenamine clear faster, which is why 48 hours is sufficient for those.
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 needed because:
- These tests measure antibodies present in the blood
- Antihistamines do not 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.
Medications containing hidden antihistamines
Some medications contain antihistamines even though they are not 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 to 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 do not 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, both short-acting (salbutamol/Ventolin) and long-acting (salmeterol), do not interfere with testing
- Topical steroid creams: These can be continued, but should not be applied to the areas where skin testing will be performed
- Most other prescriptions: Blood pressure medications, diabetes medications, and most other routine medications 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
- Maintain other medications: Continue medications for conditions like asthma or eczema, as stopping these could trigger flares
- Timing: For very young children, try to schedule testing at times when they are typically more settled; our guide to allergy testing for babies and young children covers what to expect at each age
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 blood testing instead of skin testing; the same choice arises for children, and we cover it in choosing between skin and blood testing
- Interactions: Some medications may have withdrawal effects if stopped suddenly; always consult your prescribing doctor if unsure
Practical approaches to stopping medications
Temporarily stopping antihistamines can be challenging, especially during high allergy seasons.
Managing symptoms during the medication-free period
- Time 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, 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 to 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 (such as azelastine) and eye drops should ideally be stopped before skin testing, especially if testing will be done on the face. Steroid nasal sprays can usually be continued.
"Can I take painkillers before the test?"
Most common painkillers (paracetamol, ibuprofen) do not affect skin test results and are generally safe to take. Check combination cold and flu products carefully, as some 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 accurate information possible for managing allergies effectively.
If you are booking food allergy testing, the same medication guidance applies, and the page covers what to expect on the day.
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