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Switching Medicines Safely: Why Allergens Must Be Considered

  • Allergy Aware UK
  • Aug 27
  • 2 min read

Updated: Sep 10


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Generic medicines are usually safe alternatives, but they are not always identical. Differences in inactive ingredients (like fillers, binders, adhesives, or coatings) can trigger allergic reactions. Healthcare professionals should always consider allergen profiles before switching brands. Patients and carers should insist on licensed medicines or trusted, risk-assessed brands.


Who this helps: People with allergies or sensitivities to medication excipients, their families, pharmacists, prescribers, and care staff.


Key takeaways

  • Excipients (inactive ingredients) vary between brands and can trigger allergic reactions.

  • Pharmacists and prescribers must weigh allergen risk, not just active ingredient equivalence.

  • Patients should request that prescribers specify a licensed medicine or a trusted, allergen-free brand.

  • Prescribers may be personally liable if unlicensed products cause harm due to poor labelling or inadequate safety data.


Why brand matters

Although the active ingredient is the same, branded and generic versions of a medicine can differ in their excipients (such as lactose, soya oil, peanut derivatives, colourings, or adhesives in patches). For most people, this makes no difference. But for allergy sufferers, even trace amounts of an excipient can cause serious harm.


Recent professional cases show the consequences of overlooking this. One patient suffered an allergic reaction after a pharmacist switched a branded patch for a generic equivalent without checking excipient safety. This highlights a key gap in practice: clinical equivalence is not the same as allergen safety.


Professional responsibilities

Healthcare professionals must:

  • Check excipients when switching brands or dispensing generics.

  • Communicate with patients and prescribers before making substitutions.

  • Use risk assessments where no identical allergen-free alternative exists.

  • Document and report any adverse reactions promptly.


Personal liability: When prescribing or dispensing unlicensed medicines, healthcare professionals assume direct responsibility for product safety. Unlike licensed medicines, unlicensed products may:

  • Have poor labelling standards.

  • Offer limited or unverified information about excipients.

  • Lack an approved Summary of Product Characteristics (SPC) and are absent from resources such as the EMC (Electronic Medicines Compendium).

  • In some cases, contain traces of allergens that prescribers have no reliable way of discovering.


This means prescribers could be personally liable if harm arises from inappropriate product choice — including allergic reactions linked to hidden excipients.


Patient empowerment: what you can do

  • Ask your prescriber to state the brand name on your prescription if you know it is safe for you.

  • Request reassurance that a medicine is free from allergens relevant to you (e.g., lactose, soya, peanut oil, gluten).

  • Know your excipient triggers — carry an allergy card if possible.

  • Challenge substitutions politely but firmly if the alternative hasn’t been risk assessed.

Remember: you have the right to receive medicines that are safe for your allergy profile, not just clinically “equivalent”.


When to seek help

If you experience a rash, swelling, breathing difficulty, or any suspected allergic reaction to a medicine:

  • Use your adrenaline auto-injector (if prescribed).

  • Call 999 immediately.

  • Report the reaction to your GP or pharmacist, and ask for a Yellow Card report to be submitted to the MHRA.


References

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