Most common and interesting questions we obtained into the mail.
  1. Chocolate
  2. Coffee
  3. Fruits
  4. Kernels of fruit trees
  5. Nuts and similar products
  6. Vegetables
  7. Honey
  8. Salt
  9. Tea tree oil
  10. Menthol and eucalyptus
  11. Teflon - Polytetrafluoroethylene



Chocolate is toxic for both dogs and cats, but can be dangerous also to other animal species - poisonings are described in horses, pigs, cattle, poultry etc. The health impairment and complications were described also in elderly humans with pre-existing heart diseases.

Chocolate contains caffeine and also theobromine, which is a substance similar to caffeine. Theobromine is especially dangerous to animals, because its metabolism in most of the animal species is very slow compared to humans. Thus it can cummulate in the animal organism and influence it for a very long time. Theobromine in the body influences substance called adenosine which is responsible for the regulation of heart rhythm. Once the theobromine occupies binding places which should be under normal conditions occupied by adenosine, heart dysrhytmias, which might be even fatal, occur. Theobromine also increases calcium content in cardiac cells which leads to very strong contractions of cardiac muscle. Patients with heart disease or circulatory system disease are then susceptible even to very small amounts of theobromine, healthy animals are in danger after the ingestion of bigger amounts of chocolate.

Moreover, chocolate can be dangerous also due to its high fat content. This excessive fat amount may lead to acute pancreas damage, which is very often life-threatening health complication.

Lethal dose of theobromine for healthy dog is aproximately 300 mg/kg of body weight, for healthy cat approximately 200 mg/kg of body weight, for rat approximately 800-1000 mg/kg. In rats consuming small amounts of theobroming for a long time testes damage was described.

In dark chocolate there is approximately 500 mg of theobromine in one 100 gram chocolate bar, in milk chocolate it is approximately 200 mg of theobromine in 100 gram chocolate bar.

The biggest risk of chocolate poisoning exists in ill animals, young animals and after accidents when the animal eats e.g. whole the chocolate box. If you treat your animals with small amounts of chocolate several times a day (e.g. as a training reward), the risk of poisoning is also big, as the theobromin may cummulate due to its slow excretion.



Coffee is also dangerous for animals. As well as chocolate it contains caffeine, but in a much higher concentration. On the other hand it contains only traces of theobromin, which is not responsible for the poisoning in this case.

Caffeine is another substance which occupies and blocks adenosine receptors and thus leads to heart arrhytmias. It also increases calcium concentration in heart cells and strenghtens cardiac contractions. Moreover it stimulates nervous tissue and can cause tremors and seizures in overdose. Caffeine is metabolised more quickly compared to theobromin, so the risk of cummulation is lower.

Lethal dose of caffeine in dogs is approximately 100-200 mg/kg of body weight, for cats 80-150 mg/kg of body weight. The poisoning is usually the consequence of the caffeine beverages consumption, but it is possible also from the combined medical preparations for pain management (pain killers - often with Extra in the name, -fein as the suffix of the name etc.).

The symptoms of poisoning appear faster then in chocolate poisoning and include vomiting, diarrhoea, reslessness, high blood pressure, heart arrhytmias and convulsions. Death may follow as a consequence of exhaustion or due to circulatory collapse.



Fruits are usually harmless for animals, but one kind which is provably dangerous and toxic is avocado (confirmed in birds, but the possibility of poisoning has not been excluded even in other animal species) and grapes and raisins (confirmed in dogs, highly probable in cats and ferrets, possible also in other animal species). In all the animals it is absolutely necessary to respect their natural composition of feed and if the fruits or specific fruits are not part of them, then avoid giving it to such animals. In species commonly eating fruits respect their area of origin and dont administer fruits they are not used to, exotic. Never give fruits which are immature, rotten, moldy, chemically treated.

The problem with fruits does not have to be only its toxicity, but also, especially in immature fruit, it can contain a lot of organic acid, which irritate stomach and animal can have gastrintestinal problem from it. In some mature fruits (apricots, peaches, pears, cherries), a very high content of sugars can cause digestive discomfort as those simple sugars fermentate in guts, cause diarrhoea, flatulence and colic. Its consupmtion and consequent stomac and intestine imbalance will then lead to dysbalance in microflora, dehydration, bad nutrition.

Fruits also contain a lot of vitamin C, but most of the animal species can produce this substance themselves (exceptions are guinea-pigs and primates), so they do not need it in their feed. Excessive intake of vitamin C burdens kidneys,  and its metabolites - oxalates, can contribute to kidney and urinary stones formation.

Rotten or moldy fruit very often contains patulin - mycotoxin. This substance is chronically toxic and influences amount and function of many enzymes in the body, later resulting in problems with nutrition, digestion and immunity.

Kernels of fruit trees:

Many trees from Rosaceae family, to which belong stone fruits but also apples, contain so called cyanogenic glucosides. These substances are digested and cleaved in stomach, where they release cyanide ions, which re very strongly poisonous. Cyanides block utilization of oxygen in the tissues, so eventhough the blood is full of oxygen, the animal breaths hardly and quickly, is exhausted, suffocates, later arrhytmias and cramps can occur. Many of the poisonings are lethal.

After the consumption od fruits - appricots, peaches, plums, cherries and sour cherries (sometimes also apple seeds) - including the kernels, two types of health problems can occur:
The first one is not connected with poisoning, but with the gastrointestinal problems which may develop - diarrhoea from the sugar fermentation, or constipation which may lead even to death of the animal, of it gut get obstructed with the excessive ammount of non-digestible kernels. The second one is a consequence of cyanide poisoning. Cynaides are in the trees located mainly in the bark, leaves and seeds which are present inside the kernel. Under normal conditions, if the kernel is intact, the poisoning from fruits is not possible. But when the kernel is broken - typically in over-matured fruit, after the damage by insects etc., the seeds starts to be in contact with humidity and enzymes from the fleshy part of fruit and the glucosides and cyanides are released. Consumption of free seeds or fruits already contaminated by free cyanides can lead to the poisoning.

Fatal poisonings by cyanides in pet animals are fortunately rare, in farm animals which are fed fruit remnants fatalities are more common. We recommend regular check of fruit quality in animals which are fed fruits and removal of kernels. Never let any animal eat bigger amount of the fruits in the gardens or orchard freely.

Nuts and similar products:

Macadamia nuts are proved to cause poisoning in dogs. Neither toxic substance, nor the mechanism of action is known. Clinicals signs appearing after the ingestion include vomiting, weakness, incoordination, tremors and increased body temperature. Sometimes also muscle pain and swollen joints are described. Poisoning is rarely lethal in healthy dogs, but if preceiding liver or kidney disease were described in the affected dogs, fatalities occured. Common is also severe to lethal poisoning if the the animal ingested macadamia nuts together with chocolate.  

In almonds, the problem is the content of cyanogenic glucosides. We distinguish two types of almonds - bitter (with high content of glucosides) and sweet (with low to minimum content of glucosides) varieties. Bitter almonds are nowaday not available in the Czech Republic, but there are still many countries where you can buy them for baking purposes (high temperatures remove cyanides). They should be properly labeled. In bitter almonds, lethal dose is 5 seeds for a child and 15 seeds for an adult. In sweet varieties, cyanide concetration is approximately 10 times lower, this is why they are not considered much toxic for adults. It is not recommended to give to a child more than a few pieces, animals should not be given them at all. Cyanides block oxygen utilization in tissues and the result is suffocation and death eventhough the blood is full of oxygen. 

Black walnuts/walnuts are considered toxic for horses. In the documented cases, the animals very often ate whole the nut including the soft sheath around, so it is not clear, wheteher the toxicity can be contributed to the seed inside, or whether it is due to the sheath. Still, we do not recommend giving these nuts to animals which do not have nuts in their natural feed.

There were no studies made on the safety of other nuts and dry fruits, so the knowledge on their use in animals is minimal.

General risks connected with the consumption of nuts are:
1) possible allergic reactions, even severe anaphylactic reactions
2) high content of fats and thus risk for the pancreas - possible acute inflammation of pancreas, which is very dangerous and may be life-threatening; and digestive problems, diarrhoea ve
3) if the nuts are stored inconveniently in wrong temperatures and high humidity, there is a high risk of their contamination by molds and production of mycotoxins, with consequent risk of health damage by toxic products of those molds
4) salted nuts are dangerous by their high salt/sodium content, which leads to mild to severe mineral imbalance and salt poisoning


Whole the plant of potato is poisonous. Potatoe plant contains alkaloids, the most improtant of them is called solanine. Solanine causes damage to intestines, liver, red blood cells and in higher doses can cause neurological effects. The highest content of solanine is in berries and sprouts. Even the tubers contain solanine, but its content is approximately 10 times lower than in the rest of the plant, so they are considered edible. Most of the solanine in the tuber is deposited in the 2-3 mm layer under the the surface, so humans learnt to peel the potatoes to remove most of the toxin. Cooking and boiling does not destroy the alkaloids, but the are washed away to the water around, so again, you can decrease solanine amount in the tubers this way. Anyway, the production of solanine is stress based, so any bad storage or manipulation even after pulling them out of soil can lead to their increase. This is why greenish, damaged and rotting tubers should never be used.  
Cooked potatoes are considered safe for the consumption. But still they cannot be administered to some animal species, because these animals do not posses proper enzymes for the digestion of the starch, so potatoes can cause them gastrointestinal problems.

Tomatoes do not contain solanine, eventhough it is often written in different articles, but an alkaloid called tomatine, which is very close to solanine. Their toxicity is also similar. According to scientific studies, tomatine is metabolised during the maturation of the tomato berries, so it is found in whole the green part of the plant and also flowers which are poisonous, but the mature red berry is free of the toxin. 

Onion and garlic are thought to be dangerous to toxic for animals. Poisonings are described mainly in dogs and cats, but in America, also many cases of horse intoxication are observed. Poisonings are usually due to the presence of those vegetables in the food, or because garlic used to be used as an anti-parasitic agent before chemical agents were synthesised. But its efficacy and safety are low so it is not recommended anymore.
Poisoning substances responsible for their toxicity are sulphuric agents, which influence red blood cells and the dye - haemoglobin, which is inside of them. Haemoglobin is necessary for the transportation of oxygen. Once haemoglobin is oxidized, it cannot transport oxygen and the organism starts to suffer from hypoxia. Toxicity of garlic and onion is lower in humans, this is why they are taken as common foodstaff in us. The difference in sensitivity among animal species lies in the different structure of haemoglobin in them, and also in the presence and concentration of enzymes which can repair haemoglobin. The species most susceptible to red blood cell damage are cats.
The poisoning can appear as soon as within 24 hours if the poisoning is severe, but more often, the signs of poisoning develop within a few days, when the damaged and unrepaired red blood cells start to decompose. Typical signs involve painful belly, diarrhoea, quick breathing, suffocation, tiredness and apathy. Lethal poisonings are not common, but the death by the suffocation is possible if majority of the red blood cells are affected. Also chronic poisoning from the long-term ingestion of small doses is possible, only a little, but permanently decreased levels of oxygen in the body burden all the organs. 

Broccoli is considered a relatively safe kind of vegetables for dogs. In a small amount it has positive effects, but the amount eaten should not exceed 5 % of daily portion. Excessive and frequent consumption can have negative impact on both animals and humans. All Brassicaceae plants contain substances called glucosinolates, which in higher singl-dose amounts lead to digestive problems as vomiting, diarrhoea etc. Glucosinolates also influence thyroid gland and in chronic intake disturb its function and lead to its insufficiency and growth, the result is hypetrophy of thyroid gland called struma. Fortunately are those substances at least partially destroyed by cooking. Moreover Brassica vegetables often cummulate nitrates and nitrites from the soil, which are substances influencing mineral balance in the organism and in high amounts also influence blood pigment - haemoglobin and convert it to less active product, which is not able to transport oxygen. Animals can then suffer from tiredness, nausea, breathing difficulties, apathy etc. due to the lack of oxygen in tissues.


Honey is not toxic for animals. However, even animals can have allergy to all honey-bee products including honey, so it is recommended to be careful and try it first in a very small amount. Moreover, higher amounts are not recommended anyway, as animals are not used to the high content of sugars and can suffer from diarrhoea, and also the blood glucose level can be increased, which is dangerous for diabetic patients. Due the possibility of the presence of the spores of certain microorganisms in honey, it is not recommended to give honey to sucklings and young animals.

Giving honey to animals orally has not proved to have any benefitial effect on immune system. The only use, where it has a positive impact is the treatment of small skin wounds, where it works as an antiseptic and speeds up the healing process. Other way of use which is described sometimes, but the effect was not confirmed by research, is the use of honey as a source of quick simple sugars, vitamins and minerals in the convalescence process, but the honey must be natural, crude, not pasteurized. Increase of the temperature during pasteurization leads to the loss of many important and active enzymes and peptides. Even in the cases described above always consult honey administration to an animal with your veterinarian and avoid giving more then 10 grams of honey per 10 kilograms of weight of the animal.


Salt is of course a natural and necessary stuff for all organisms as we need sodium ions, but its higher amounts are very toxic. Common diet is sufficient for replenishing of our body requirements. Dog commercially manufacterd higher quality granules usually contain approximately 0,5 % of salt, which is optimum.

The lethal dose for a dog is approximately 4 grams of salt per kilogram of body weight, in cats it is much less (exact dose is not given in the literature). The symptoms of overdose and poisoning of course appear even in lower doses the lethal.

Salt poisoning is very treacherous, as most of the symptoms of intoxication may appear as late as 1-2 days after the ingestion, and the damage to kidneys and brain in such time is very often serious and it might be late for the treatment.

Salt poisonings in domestic animals are described mainly in dogs, typically after ingestion of home-made or commercially made modeling clays (usually called play dough), which is formed by 25 or more percents of salt. Moreover the poisoning appears after the ingestion of road salt or the pickle for meat preservation. These salt poisonings are often fatal.

Human foodstuff, especially sausages and similar meat products which contain preservation salts and other chemicals, are also a possible source of salt poisoning in animals. They often contain also nitrites, which are very dangerous, cats are more sensitive to their action. Important condition of  this type of salt poisoning is usually the concurrent lack of water, so always check, whether there is sufficient fresh water available to your animal. If it is not accessible, frozen, lacking, etc.,  the risk of poisoning is much higher.  This type of salt poisoning is rarely fatal, but the excessive amount of salt irritates stomach, guts, disturbes mineral balance in the organism and overloads kidneys which might be then susceptible to kidney stones formation and failure.

 Tea tree oil:

It is known about tea tree oil that it is toxic for cats, and also several cases of children poisoning by this substance were described. Very often also allergic skin and whole body reactions to it are seen.

In general, it is necessary to avoid ingestion of tea tree oil in both humans and animals, and the application on bucal mucosa should be in the minimal possible amount and only for a short time. 

After ingestion, the poisoning is quicker and stronger. The sources differ in the description of symptoms, but problematic coordination, muscle weakness, hypothermia, depression, liver damage and ocassionally even collapse and death may appear. Fatal cases were decribed especially for cats and only one case for guinea pig.

In topical application, the poisoning is possible too due to the good solubility of active substances in lipids and oils and good absoption through skin to the organism. In higher doses or through wounds it may lead even to the systemic syptoms of poisoning.

Another problem connected with tea tree oil is, that it is unstable when exposed to UV light, active substances are then decomposed into different products which are harmful and are know to cause allergic reactions on skin. Thus it is necessary to store tea tree oil in dark places.

Tea tree oil is not recommended for cats, pregnant animals, young animals, weakened animals. Never use it in higher amounts on open wounds. Use it only for topical application. In case you reveal symptoms of allergy or poisoning, wash the skin with soap and lots of water and visit your veterinarian. Do not use tea tree oil anymore in animals who had negative reaction to it.

Menthol, eucalyptus:

Eucalyptus and menthol are considered harmful for animals. Fatal cases of poisonings by so called essential oils (eucalyptus oil, mint oil and menthol, limonen and linalol, citronella oil, cinamon oil etc.) are fortunately described only rarely, but milder form of poisoning by these substances is very common.

The symptoms are usually vomiting, diarrhoea,drowsiness, after higher amounts also tremors and cramps. In chronic intake liver damage follows. Especially sensitive are cats who lack one important enzyme for the metabolism and excretion of those substances from the body.  

Teflon - Polytetrafluoroethylene:

Teflon is a substance toxic especially for birds. This substance is used in the dishes - e.g. frying pans, but also in hair dryers, soleplates of irons, etc. The warning about the contents of teflon is usually included in the manual/leaflet of the product. In some products, especially dishes, it is even written that the fumes from teflon are toxic to birds.

Under normal conditions of use, teflon does not relaese visible fume, but even in the working temperatures around 240 °C, teflon starts to release invisible vapour and microparticles. They can be problematic even for humans and other animals, but only in very high amounts and especially after chronic exposition. In contrary, birds are sensitive even to very small amounts after acute exposure. We do not know the exact mechanism of action, but the symptoms of poisoning are breathing difficulties, movement problems, and quick death (within  a few minutes) is possible and quite common. This is why this poisoning is practically incurable, there is no time for the transportation of the bird to the vet and for the treatment.

In case the poisoning is only mild, take your bird to the fresh air (out of the building, next room is not sufficient) and call your veterinarian. In case he/she has it, he may administer oxygen inhalations, and antibiotics to prevent bronchi and lung inflammation.

In general, it is not recommended to keep any animal (not only birds, but also small rodents, reptiles etc.), which is kept permanently in the cage, in the kitchen.  In case of teflon substances release or if something is burnt and toxic products are released into the air, they have no possibility of escape. Animals who live in cages must be kept in the well ventilated rooms where they will not be exposed to any vapours and other toxic substances.