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Overview: Drug allergies

Last Update: August 14, 2023; Next update: 2026.


Medications can have various side effects, including allergic reactions. These occur if the immune system considers the medication to be a harmful substance, and fights it. A drug allergy is not the same as a drug intolerance, which is where your body's metabolism can't process the medication properly.

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.

At a glance

  • Drug allergies can cause skin rashes, itching and swelling.
  • The reaction may be immediate or delayed.
  • It can be treated with steroids or antihistamines.
  • If there are signs of an anaphylactic reaction, call an ambulance right away.
  • It is often possible to avoid drugs that cause allergies.


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 weeks.

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.

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 agents),
  • local anesthetics,
  • general anesthetics,
  • medication for the treatment of cancer (chemotherapy),
  • medication for epilepsy,
  • psychiatric medication (antidepressants or neuroleptics),
  • ACE inhibitors for the treatment of high blood pressure, and
  • additives in medication.

Medications that are given through a drip (an infusion) or injection, or those that are absorbed by the skin, are more likely to cause allergic reactions than those that are taken in the form of tablets or a liquid. 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. Skin rashes can be caused by a lot of medical conditions and other allergies too.

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 different 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 these to be medications, they can cause allergies too.

There are different types of allergy tests:

  • Skin prick test: This test checks whether the immune system overreacts to certain triggers. Solutions of potential allergens are put on the forearm with enough space between them. The skin is gently pricked so the solutions can get into the skin. The skin is then observed to see whether it turns red or itchy and bumpy.
  • Patch test: 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.
  • Blood test: A sample of blood is taken in order to find out whether the body has made antibodies to a medication.
  • Provocation test: 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.

Although various tests can be done, it is sometimes still difficult to find out the cause for sure.


It is often possible to simply avoid medications that are causing allergies, or use other medications instead. But there’s no treatment that will make drug allergies go away again in the long term: Allergen-specific immunotherapy (desensitization) isn’t a treatment option for this kind of allergy.

Immediate allergic reactions can be treated using steroids or allergy medications called antihistamines. More severe reactions are treated with adrenaline (epinephrine) injections and steroids. If there are signs of an anaphylactic reaction, it’s important to call the emergency services right away (112 in Germany and many other countries, 911 in the U.S.).

People who have a confirmed drug allergy can talk with their doctor about which other medications they could use instead. Cross-reactivity should be taken into account too. This is where you also react allergically to other substances that have a similar structure.

It is quite easy 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 or painkillers, for example. But 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. Then the doctor and patient have to carefully consider which option has more advantages: avoiding or taking the medication.

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People who have drug allergies are advised to always carry a medical ID card or bracelet on them, listing the medications that they are allergic to. This will allow doctors to use the information 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

Research has 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, that increases the risk of bacteria becoming resistant to the drug. So it’s important to try to find out for sure whether you actually have a drug allergy or not.

Further information

When people are ill or need medical advice, they usually go to see their family doctor first. You can read about how to find the right doctor in our topic "Health care in Germany" – and our list of questions can help you to prepare for your appointment.


  • Bamanikar A. A Review of Drug Allergies: Diagnosis and Management. EMJ Allergy Immunol 2016; 1(1): 52-57.
  • Deutsche Gesellschaft für Allergologie und klinische Immunologie (DGAKI). Leitlinie Allergologische Diagnostik von Überempfindlichkeitsreaktionen auf Arzneimittel (S2k-Leitlinie, in Überarbeitung). AWMF-Registernr.: 061-021. 2014.
  • National Institute for Health and Care Excellence (NICE). Drug allergy: diagnosis and management (NICE Clinical Guidelines; No. CG183). 2014.
  • Warrington R, Silviu-Dan F. Drug allergy. Allergy Asthma Clin Immunol 2011; 7(Suppl 1): S10. [PMC free article: PMC3245433] [PubMed: 22165859]
  • IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

© IQWiG (Institute for Quality and Efficiency in Health Care)
Bookshelf ID: NBK447110


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