Ben the Vet

Toxic Substances

Common Intoxications of Cats and Dogs

an information sheet for dog owners

Christmas can be a dangerous time for pets for various reasons: Firstly, during the festive period our lives generally become busier and we have less time to consider the risks in our own households. Secondly, it is a time for indulgence in food, drink and gifts – we tend to eat things that we may not for the rest of the year and also have more things lying around the house. We also have more visitors, who may not be aware of what pets should and should not be fed and to where your dog is allowed access. Finally, we all tend to anthropomorphise a little and feel that the dogs must be feeling left out of the celebrations, tempting us to treat them with things that we normally wouldn’t consider.

I would like to bring some common (and some not so common) toxic substances to your attention in order that you and your pets may enjoy the festive season with no veterinary problems.

Furthermore, I will also mention some other festive hazards which, although strictly speaking aren’t toxic, may cause their own problems.


Chocolate: One of the worst culprits, chocolate contains theobromine – a substance similar to caffeine, which causes nervous system, cardiac and respiratory hyperactivity. Signs range from vomiting and diarrhoea to convulsions and acute collapse. The toxicity depends on the cocoa content of the chocolate – so dark chocolate is far more toxic than milk chocolate. The lethal dose varies greatly between individuals, but there is no hard and fast rule and two individuals of identical body weight and age may have different tolerance levels. An average sized bar of good quality dark chocolate may be sufficient to kill an Irish Setter. The toxicity is rapid and often irreversible.

Onions: In sufficient quantity, onions can cause red blood cell damage and an anaemic crisis.

Alcohol: Similar effects to those seen with excess in humans. It is simply not fair to subject an animal to this.


Holly: This common Christmas decoration causes gastro-intestinal signs, such as vomiting and diarrhea.

Ivy: Causes profuse salivation, vomiting, abdominal pain and diarrhoea.

Mistletoe: Far from romantic – the toxins in the leaves or berries cause prolonged vomiting, which may be delayed by as much as 24 hours after ingestion of the plant.

Poinsettia: Mildly toxic. The sap is irritant to the mucous membranes and skin.

Amaryllis, Irises, Tulips: All may result in moderate gastro-intestinal signs.

Lilies: Can be toxic to the kidneys (nephrotoxic) and also to the heart (cardiotoxic). Signs may be delayed and treatment must be started early to avoid potentially fatal kidney failure.

Jerusalem Cherry: Cardiotoxic – reduces heart rate and may cause heart rhythm disturbances.

Foxgloves, lily of the Valley, Oleander: All cardiotoxic.

Azaleas: Severely toxic and frequently fatal, via cardiotoxicity.

Yew: Rapidly fatal – causes vomiting, diarrhoea, weakness, slow heart rate and convulsions. In some cases death occurs within minutes of ingestion.

All parts of the tree are toxic except, surprisingly, the ‘berry’.

Other toxicities:

Nicotine: From any form of tobacco or nicotine replacement gum or transdermal patches. This is rapidly toxic and can cause hyperexcitability, vomiting, nervous system and cardiac abnormalities and eventually respiratory arrest and death.

Antifreeze (ethylene glycol). An extremely toxic substance that, unfortunately, seems to be pleasantly flavoured for animals. Just over one teaspoonful may be fatal for cats. Dogs are a little more resistant– the minimum fatal dose for a 25kg dog would be about 150ml. In the first phase signs occur rapidly and include disorientation, ‘drunken behaviour’ and vomiting. The second phase causes severe metabolic abnormalities 12-24 hours after ingestion. The third phase is irreversible acute kidney failure. Therapy can really only be effective if started within the first six to eight hours.


Please don’t forget to keep turkey bones and other cooked bones out of reach of your dog. Apart from causing diarrhoea and being a choking hazard, sharp shards of bone may penetrate the oesophagus (gullet) or other parts of the gastrointestinal tract causing serious damage.

Remember that your dog can enjoy the excitement of Christmas without indulging in the food. We all like to treat our dogs but, as you know, Setters are prone to colitis (large-intestinal diarrhoea) and changes in diet are a major factor in this problem. Feed your dog as normal and you should avoid ruining their Christmas and yours.

Instead of giving them human food, treat them to something they will really appreciate, such as a new chew or toy.

Top tips:

1.     If your dog does eat something toxic, or even if you suspect this, contact your vet immediately. All vets must provide emergency cover for the holiday period and out-of-hours.

2.     If your vet tells you to try to induce your dog to vomit after an intoxication, before going to the surgery, you can try one of the following:

a.      Soda Crystals – a few of these given by mouth often causes vomiting.

b.     Mustard – smear a teaspoonful on the back of the tongue.

3.     To keep your dog occupied and amused during the festive period, stuff a Kong with healthy treats (i.e. soaked dry dog food or Kong stuffers).

If your dog does have diarrhoea due to over-indulgence, feed a diet of boiled rice and low-fat cottage cheese for a couple of days, before gradually reintroducing their normal diet.

Benjamin Harris MA VetMB (Cantab) MRCVS