Recognize the urgent symptoms
NHS guidance warns that a serious allergic reaction can involve sudden swelling of the lips, tongue or throat, difficulty breathing or swallowing, or loss of responsiveness. Call your local emergency number immediately for these symptoms. Do not drive yourself or wait to see whether the person simply sleeps it off. [1]
The complete product matters
A tablet, gummy or liquid contains ingredients beyond the named active substance. A reaction occurring after a product does not, by timing alone, identify which ingredient caused it. Keep the packaging for medical assessment and do not test the suspected product again at home to confirm an allergy. [1][2]
Distinguish ordinary adverse effects from a suspected allergy
Imagine mild next-day sleepiness occurs without swelling, rash or breathing symptoms. That can be a known adverse effect rather than evidence of allergy, but it still matters for driving and other activities. Conversely, swelling and breathing difficulty require urgent care even if the product has been taken before without a problem. [1]
| Situation | Response or distinction |
|---|---|
| Swelling with breathing difficulty | Emergency assistance now |
| Next-day drowsiness alone | Can be a nonallergic adverse effect |
| Suspected product | Keep packaging for clinical review |
Sources for this article
- Side effects of melatonin - NHS
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product. - Circadin 2 mg Prolonged-release Tablets - Patient Information Leaflet (PIL) - (emc) | 2809
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product.