Poisoning after European adder bites

Responses to adder bites are often mild, but in some cases they can cause severe poisoning. To assess the risk, it is important to be aware of the signs of severe responses and their development.

Viper can cause severe poisoning, it has a dark zigzag band along the back

Common European viper

The Norwegian Poison Information Centre can provide guidance and advice regarding adder bites. Call 113 in the event of dizziness or fainting shortly after being bitten.

Symptoms of mild adder poisoning

The severity of the symptoms will depend on the amount of poison that gets into the body. In the case of many bites, the amount injected is minimal, and little or no reaction occurs. These are known as ‘dry bites’.

Adder bites are often two dot-shaped stings spaced 3-9 mm apart. In the case of dry bites, there need be no more than a very mild reaction around the site of the bite, and healthy young people and adults can often monitor themselves at home.

Mild reactions are slight swelling and bluish discolouration around the site of the bite, and the person may feel slight discomfort. In the case of mild adder poisoning, these symptoms will not worsen. Monitor developments for at least 6-8 hours after the bite, and contact the Poison Information Centre or doctor in the event of any deterioration. Follow the advice for “First aid following an adder bite”, even if you suspect a dry bite with mild symptoms.

Symptoms of severe adder poisoning

A large amount of poison can cause severe poisoning in anyone. The severity also depends on your weight, health, age and where on your body you are bitten. The symptoms will often develop rapidly (within 1-2 hours), frequently starting with systemic effects such as dizziness, fainting and/or difficulty breathing. Gradually, you may see a severe local reaction develop, with swelling and discolouration of the skin around the bite. Such cases should be observed in hospitals, and often need to treated with an antidote.

If you experience severe symptoms soon after being bitten, call 113 so you can get to hospital quickly.

Reactions in the tissues around the bite often become apparent within 6-8 hours after being bitten, and the symptoms can continue to develop after this. Anyone who thinks they may have been bitten by an adder should keep an eye on the area around the bite for the next few hours.

The reactions can develop gradually and affect the entire body part (e.g. the entire leg or arm), and possibly even the entire body in very severe cases. In this case, hospital treatment will be necessary, and an antidote may be necessary. An example of a serious development in symptoms is a swelling which spreads out from a bite on the hand to the elbow within a few hours. Severe local reactions can develop either with or without early systemic reactions.

First aid following an adder bite

Call 113 if you experience symptoms such as vomiting, dizziness, fainting, difficulty breathing or swelling which develops rapidly.
Otherwise, if necessary, you should contact the Poison Information Centre for advice on what to do next and treatment.

  • Do not touch the bite site (do not squeeze, cut or suck on the bite)
  • Keep the bitten body part still and, if possible, in an elevated position, even while travelling to the emergency medical service/hospital
  • Remain as still as possible; children should be carried to the vehicle if possible. If you are bitten when you are a long way from civilisation (in the mountains or a forest, on an island, etc.), you should travel to somewhere more central. Move as calmly as possible and ask for assistance if you need it
  • In the event of the onset of swelling, use a pen to mark the outer rim of the swelling and make a note of the time, to make it easier to keep track of developments
  • A tetanus vaccine or booster dose may also be appropriate under current guidelines for individuals who can monitor themselves at home (speak to a doctor/paramedic). This vaccine/booster dose should ideally be administered within 12 hours after the adder bite

Who can monitor a bite at home?

  • In most cases, healthy young people (aged 12 or over) and adults who have been bitten in the arm or leg and only experience mild reactions during the first few hours after being bitten can monitor themselves at home. Contact the Poison Information Centre for advice if necessary
  • Healthy young people (aged 12 or over) and adults who have only experienced mild local reactions 6-12 hours (or more) after the bite without any signs of deterioration
  • Children (under 12), the elderly (from around 70 upwards) and pregnant women who experience only minimal systemic or local reactions 12-24 hours after the bite can often monitor themselves at home. Contact your doctor or the Poison Information Centre for assistance with assessment and guidance if necessary

Who should see a doctor/go to a hospital for assessment?

  • Children (under 12), pregnant women and the elderly (from around 70 upwards) should normally be assessed by a doctor/at hospital
  • Anyone (including both children and adults) who develops systemic or anything more than mild local symptoms after being bitten. In the event of rapid deterioration, call 113
  • Anyone who has been bitten elsewhere other than on their arms or legs, such as the head region, chest, abdomen or back
  • Anyone with an underlying illness/reduced general condition, or who takes ACE inhibitor blood pressure medicine (as of September 2021, these are medicines with the active substance enalapril, lisinopril, captopril, perindopril or ramipril)

Hospital treatment

  • Doctors will monitor developments and treat any symptoms as and when necessary. Administration of an antidote may be appropriate
  • Tetanus vaccine or a booster dose of this vaccine will be given in accordance with applicable guidelines. This is most effective in the early stages after the bite

Think you may have been bitten by an adder several days or even weeks ago?

Many people realise they may have been bitten by an adder long after they think it may have happened. The Poison Information Centre advises many people who think they may have been bitten several days ago. We consider these cases based on the sequence of events. In most cases, medical attention is not necessary, but some situations require examination and treatment.

Healthy young people and adults can normally monitor themselves at home if at least eight hours have passed since the bite and there have only been mild symptoms with no signs of deterioration. The elderly, pregnant women and anyone with an underlying medical condition should under any circumstances contact a doctor or alternatively the Poison Information Centre for assessment and advice up to 12-24 hours after a possible bite.

How long does adder poisoning last?

Severe adder poisoning can require many days of hospital treatment. After such treatment (either with or without administration of an antidote), it will normally take weeks to months for the arm or leg to fully regain its normal function.
Even in case of mild adder poisoning, it may also be a long time before you recover fully, but the symptoms will normally be milder in such cases.