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10 medication allergies FAQs


WebMD Medical Reference
Medically Reviewed by Dr Rob Hicks

What is a drug side effect?

Side effects are a drug's undesired effect – they are also known as 'adverse events'. However, during the development of certain drugs these unexpected reactions can, on occasion, prove to be effective in the treatment of other conditions, different to the one originally being investigated.

Are side effects dangerous?

The side effects of some drugs can be serious as all drugs are chemicals with a potential for producing severe, toxic reactions. People are genetically different and, as a result, their responses to drugs differ.

Symptoms of a side effect can range from mild to life-threatening. Many medications can cause common side effects, such as an upset stomach or headache. The side effects may disappear as the body gets accustomed to the drug. If side effects persist, a doctor may review the dosage, or the time between administering a dose may be increased.

The Medicines and Healthcare products Regulatory Agency (MHRA) states if a side effect is described as 'very common' it means that more than one in 10 people taking the medications are likely to experience the side effect.

Can side effects affect the whole body?

When a drug is taken it is sometimes distributed throughout the body, so the effects are not restricted to one organ or tissue.

How can I reduce the risk of side effects?

Take your medicines exactly as prescribed by your doctor or pharmacist and follow the dosage instructions on the pack. The patient information leaflet will tell you about any known risk factors and what you can do to reduce the chance of side effects. You may be able to lower the risk of side effects, for example, by not drinking alcohol or not eating certain foods during your course of medication.

What is a medication allergy?

Allergic reactions are not a dose related side effect of a drug; the symptoms are similar to those caused by other allergens and in extreme cases can cause anaphylactic shock.

What happens during an allergic reaction?

The immune system mistakenly responds to a drug as if the drug is a threat to the body. The immune system recognises the drug as a foreign substance and the body produces certain chemicals, such as large amounts of histamine, in an attempt to expel the drug from the body.

During an allergic reaction, the release of histamine can cause symptoms like hives, skin rash, itchy skin or eyes and congestion. A more extreme reaction may cause anaphylactic shock, which requires immediate medical attention. The symptoms appear in minutes and may include difficulty breathing, blueness of the skin, a blotchy red rash, fainting, anxiety, rapid pulse, nausea and swelling in the mouth and throat.

What are the most common drugs people are allergic to?

Common drugs people are allergic to are antibiotics, such as penicillin. Other drugs commonly found to cause allergic reactions include anticonvulsants and iodine (found in many X-ray contrast dyes).

If you have known drug allergy you should always inform your doctor before undergoing any type of treatment, including dental care. It is advisable to wear a medical alert bracelet or pendant, or carry a card that identifies your allergy.

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