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Medications can have a number of side effects, including allergic reactions. Allergies occur when the body’s immune system overreacts: It considers the medication to be a harmful substance, and fights it. Drug intolerance occurs if the medication can’t be properly metabolized (processed) in the body.

People who have a drug allergy are often no longer sure which medications they can take, and which medications they can’t take. And it isn’t always easy to find alternatives to the medications you’re allergic to. So drug allergies not only cause acute symptoms, but may also delay treatments. Some people have to use less effective medications instead.


The symptoms of a drug allergy usually appear within one hour of taking the medication. But the reaction sometimes occurs later – after several hours, days or even months.

The symptoms that start soon after taking medication may include the following:

  • Red and unusually warm skin
  • A blotchy rash
  • Hives (nettle rash)
  • Itching
  • Swollen mucous membranes
  • Fluid retention in the body’s tissues (edema)

Severe allergic reactions (anaphylactic shock) can lead to breathing difficulties, confusion and drowsiness, or even cardiac arrest.

Delayed reactions usually occur within a few days. Only rarely do they occur up to two weeks later. They may be accompanied by a skin rash and fever. In rare cases the allergic reaction may be so severe that organs become damaged, large areas of skin peel off, or the face becomes very swollen.

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Causes and risk factors

The drugs that most commonly trigger drug allergies include:

  • antibiotics (often penicillin),
  • anti-inflammatory painkillers (NSAIDs) such as ibuprofen and acetylsalicylic acid (the drug in medications like Aspirin),
  • dyes used in imaging techniques (contrast media),
  • local anesthetics,
  • other anesthetics,
  • medication for the treatment of cancer (chemotherapy),
  • medication for epilepsy,
  • psychotropic medication (antidepressants or neuroleptics),
  • ACE inhibitors for the treatment of high blood pressure, and
  • additives in medication.

Drug allergies are more likely to occur if they are given in a drip into a vein (an infusion), injected or absorbed into the skin rather than taken orally (swallowed). Severe reactions are most common when medications are given in a drip.

Drug allergies mainly affect young and middle-aged adults. They’re more common in women than in men. The risk is higher in people who have certain genetic changes (mutations) or viral illnesses such as HIV.


A description of the symptoms usually isn’t enough to say for sure whether or not someone has a drug allergy. The symptoms are often similar to those caused by other side effects or medical conditions. For instance, skin rashes can be caused by infections such as measles or rubella (German measles).

The doctor will first ask you about the type of symptoms you had, what situations they occurred in, which medications you had taken, and when you had taken them. Some people take a lot of medications. It is then particularly important to know exactly which medications were taken, for instance based on the patient’s records or hospital discharge papers.

It is generally always important to tell your doctor about all of the medicines you are using – even herbal products or dietary supplements. Although some people don’t consider them to be medications, they can cause allergies too.

Tests can help to narrow down the list of possible allergy-causing drugs. But it is often still difficult to determine the cause for sure. Skin tests and blood tests can be done to find out whether the immune system is overly sensitive to certain triggers. Two main types of skin tests are used: Either a solution containing a food protein is put on an area of skin that has been gently scraped, and the skin is observed in order to see whether it turns red or itchy. Or the substance that is thought to be causing the allergy is placed on the skin with the help of a patch, which is then removed after one to two days to see whether there are signs of an allergic reaction (patch test). In the blood test, the doctor checks whether your body has produced certain antibodies to a specific medication.

Sometimes a provocation test is considered too. Here, the person who is thought to have a drug allergy is given a small amount of the drug, and the amount is then increased. This is done to see whether it triggers an allergic reaction, under the supervision of a doctor. Because provocation tests can sometimes cause severe allergic reactions, they are usually carried out in a hospital and may take several days. But provocation tests can’t be done for some medications, or if there’s a risk of certain – sometimes life-threatening – reactions occurring.


It’s often possible to simply avoid medications that are causing allergies. But there’s no treatment that will make drug allergies go away again: Allergen-specific immunotherapy isn’t a treatment option here.

Immediate allergic reactions can be treated using steroids or allergy medications called antihistamines. More severe reactions are treated with adrenaline (epinephrine) injections and steroids.

People who have a confirmed drug allergy can talk with their doctor about whether there are any alternatives. Cross-reactivity should be taken into account too. This is where you also react allergically to other substances that have a similar structure.

It’s possible to avoid a medication if you don’t necessarily need it. Or if there are alternative medications that have a similar effect and work just as well. This is usually the case with antibiotics and or painkillers, for example. It’s harder to avoid medications if you really need them and there aren’t any suitable alternatives – or if the alternative options are associated with risks of their own.

People who have drug allergies are advised to carry a medical ID card or bracelet on them, listing the medications that they are allergic to.This will allow doctors to react more quickly in an emergency.

Sometimes people have to take a medication that they are allergic to – such as a medication for cancer or a serious infection – because there are no alternatives. Then the following can be done: The medication is first taken in low doses under medical supervision, and the dose is then gradually increased. The doctor observes how well the medication is tolerated. The aim of this approach is to help the body to tolerate the medication better, at least temporarily. But it isn’t entirely risk-free.

Everyday life

Studies have shown that some people mistakenly believe that they have a drug allergy. They are quick to think that side effects are symptoms of an allergy – when taking antibiotics, for instance, which often cause a skin rash. But rashes aren’t always caused by allergies.

A lot of people think that they or their children are allergic to penicillin, for example. But when they do an allergy test, it usually doesn’t turn out to be an allergy after all. Penicillin allergies are actually not as common as many believe.

Mistakenly believing you have a drug allergy can have disadvantages if you avoid effective medications as a result. For instance, if you avoid using penicillin and instead use broad-spectrum antibiotics against a range of bacteria, the risk of bacteria becoming resistant increases. So it’s important to try to find out for sure whether you actually have a drug allergy or not.