I’m Corey and I’m a licensed vet. I know first hand how dogs have a tendency to eat any food they can find, even if it’s not good for them.
It’s up to all dog owners to make sure our furry friends don’t find any food that may be harmful to them.
There are a couple of food ingredients that dogs should avoid due to their antinutritive or toxic properties.
While some of these food items will not kill your dog when eaten in small amounts, moderation is rarely dogdom’s strongest suit.
It is better to avoid them completely before your dog develops a taste for them.
Grapes and raisins
Grapes and raisins are tasty and harmless to humans, however, an unknown toxin found in grapes causes kidney failure and even death in dogs.
Symptoms shown by poisoned dogs include vomiting, abdominal pain, tremors, seizures, and reduced urination. It is suggested to take your dog to the vet after ingesting any amount of grapes or raisins.
Another unknown toxin, found in macadamia nuts, affects the musculo-skeletal, digestive, and nervous systems causing locomotory difficulties, weakness, trouble breathing, tremors, paralysis, and elevated body temperature.
This type of poisoning is rarely fatal but it can be incredibly painful for the dog.
Chocolate contributes to one-quarter of all dog poisonings.
The toxins in chocolate are well known; Methylxanthines (theobromine and caffeine) affect the gastrointestinal tract causing vomiting, which is followed by episodes of hyperactivity.
If not treated by a veterinarian these symptoms evolve to heart attack, seizures and even death.
The higher the cocoa solids in chocolate, the more toxic it is to dogs – so when it comes to dark or baking chocolate, the toxic amount is much smaller than for milk or white chocolate.
Onions and garlic
Sulfoxides and aliphatic sulfides are found in all members of the allium family (ex. onion, garlic, leek, chives, shallots).
Feeding these ingredients to dogs, even in small amounts, can have a cumulative effect over time. These toxins destroy the red blood cells, causing hemolytic anemia.
The first symptoms usually seen are vomiting, diarrhea, abdominal pain and depressed behavior.
These are followed by more serious symptoms like weakness, lethargy, breathing difficulties, elevated heart rate, jaundice and even death.
Take special care when feeding your dog baby food as these products can have high amounts of these ingredients. There is no antidote for this kind of poisoning. 
A small amount of peanut butter is usually safe for dogs. However, many manufacturers add xylitol to their peanut butter formula, so make sure to read the label carefully!
Xylitol is very toxic to dogs.
Peanut butter is also high in calories and fat, leading to obesity. The high-fat content in peanut butter can also lead to pancreatitis when a dog eats a lot of it in one go.
Most manufacturers also add excessive amounts of salt to peanut butter. 
Bread or pizza dough
Yeast in the dough can cause the dough to expand in the stomach, exactly as it would in your kitchen.
This can cause bloat and gastric torsion which results in extreme abdominal pain, difficulty breathing, and leads to emergency surgery in most cases.
Dogs and alcohol don’t mix well; fermented foods, sour dough, and fermented drinks all pose a risk.
Ethanol found in these food items inhibits the nervous system’s GABA receptors, similarly to when humans get drunk but much more severe.
This leads to ataxia, sedation, hypothermia, difficulty breathing, liver failure, coma, and eventually death.
Unfortunately, our dogs cannot share our love of avocado. Avocado contains a toxin called persin to which dogs are particularly sensitive.
The whole avocado plant is toxic – fruit, pit, and leaves.
Persin causes fluid accumulation in the lungs and heart leading to difficulty breathing and heart failure.
Coffee and tea
Caffeine, like theobromine in chocolate, is a methylxanthine and is toxic to dogs.
When ingested in sufficient amounts it causes abnormal heart rhythm and respiratory difficulties.
Caffeine is found in tea, coffee and even in some green and herbal teas. 
Gum and candy
One should never give candy or chewing gum to dogs. Candy contains an enormous amount of refined sugar which can lead to high blood sugar levels and hyperactivity.
When given to your dog regularly, candy can lead to obesity and diabetes.
Xylitol is also often found in candy and chewing gum. Xylitol toxicity is characterized by an acute drop in blood sugar levels resulting in depression, inability to move, seizures, coma, liver failure, hemorrhage, and if not treated, even death. [1, 9, 13, 14]
The problem with rhubarb is that it contains oxalates.
Unfortunately, these cannot be destroyed by cooking or any conventional process. Oxalates act as an anti nutritive factor by binding calcium and other minerals causing bone weakness and mineral deficiencies.
In contrast to some of the other foods mentioned, persimmons are not fatally toxic.
They do however have a laxative effect on dogs, which is not very desirable.
The seeds and fibers can be a serious hazard since they can cause intestinal upset and blockage, but are not inherently toxic. 
Leaves and seeds/pits of apples and stone fruit
While the fruit flesh of apples, peaches, plums, and cherries is safe for your dog to eat, care should be taken to remove all leaves, stems, seeds, and pits.
These parts contain amygdalin.
Feeding your dog dairy is not a matter of life and death, and can actually be a nutritious treat if fed in small amounts.
However, dogs cannot digest dairy products, as well as most humans, do, as they usually lack the enzyme lactase.
Salt or salty foods
Salt is a case of too much of a good thing becoming a bad thing. A certain amount of salt is important for normal bodily functions.
However, human foods commonly have an excessive amount of salt for taste or preservation purposes. Salt poisoning also commonly occurs when giving your dog salt to induce vomiting.
This trick is very dangerous and it is better to take your dog to the vet than making things worse for your dog.
Symptoms of salt poisoning are severe dehydration, liver failure and brain edema leading to brain hemorrhage.
Nutmeg contains myristicin. Myristicin is structurally similar to mescaline and causes neurological and locomotor impairment.
The symptoms presented are usually an elevated heart rate, tremors, nausea and confusion.
The fruit skin and other parts of citrus plants contain essential oils and psoralen. These cause vomiting, diarrhea, skin rash, depressive behavior and muscle tremors.
The fruit’s flesh is edible. It is however very acidic and feeding your dog a lot of it can still be harmful.
Mints and breath fresheners
Many mints and breath fresheners contain menthol.
Menthol irritates the dog’s mouth and intestinal lining and could possibly cause intestinal upset. Many of these products also contain xylitol, whose serious effects have already been discussed earlier. 
Xylitol is not the only sweetener that is toxic to dogs.
Sorbitol is a laxative and causes diarrhea. While this is not as serious as in the case of xylitol toxicity, it can still cause dehydration and ion deficiency if its effects are prolonged.
Sorbitol is commonly found in sugar-free and low-calorie foods. 
This commonly used herb contains eugenol.
While it will enhance the flavor profile of your food, the eugenol they contain will cause vomiting and diarrhea in dogs. Vomiting is considered a major route of chloride ion loss.
Bay leaves are also not very digestible and can cause intestinal obstruction if a lot of them are swallowed whole. 
Oregano, marjoram and mint
The essential oils found in oregano and marjoram cause gastric and intestinal irritation in dogs.
Caraway seeds (a.k.a. Persian Cumin)
Caraway seeds are rich in the monoterpene compounds carvone and limonene.
These monoterpenes, together with essential oils, cause a mild intestinal upset and cause vomiting and diarrhea. 
Anything with THC
As legislation surrounding cannabis and its products is being revised around the world, cases, where dogs ingest this plant or its edibles, is becoming increasingly common.
THC found in cannabis causes vomiting, depressive behavior, lack of coordination, low blood pressure, dilated pupils, and low body temperature.
Tremors, seizures and coma were sometimes observed in extreme cases.
If this happens, it is always wise to take your dog to the vet sooner rather than later and to be honest about your dog’s consumption. 
Fresh chamomile flowers contain bisabolol, chamazulene, anthemic acid, and tannic acid.
While these molecules are fewer in dry chamomile, it is still not suggested to give to dogs.
These toxic molecules cause vomiting, diarrhea, anorexia, dermatitis and allergic reactions. Their long term use can lead to increased bleeding tendencies. 
Licorice’s distinctive flavor comes from glycyrrhizin.
Glycyrrhizin, in high enough doses, can be toxic to dogs. Glycyrrhizin acts like aldosterone, a hormone found in the body that helps regulate potassium levels.
Commercially available beef jerky has extremely high salt content, contains a substantial amount of artificial preservatives (depending on country of origin), and contains a lot of spices (ex. onion and garlic).
The negative effects of most of these ingredients have already been discussed.
Dogs can, however, enjoy homemade jerky that contains no salt, spices or additives (100% meat). 
Cinnamon sticks and extracts are rich in essential oils that can cause irritation of your dog’s skin, mouth, and digestive system.
It is also not suggested to give your dog powdered cinnamon as its fine powder can easily be inhaled causing irritation of the nasal passages, trachea, and lungs.
In severe cases, this can lead to aspiration pneumonia. 
Avoid giving your dog any spoilt food, as well as keeping your bins safe from thievery. Some molds can produce tremorgenic mycotoxins, causing tremors and seizures.
These kinds of molds can grow on almost any type of spoilt food – so don’t give your dog anything you wouldn’t eat yourself.
Moldy cheeses might not cause you harm but can harm your dog. Blue cheese contains Roquefortine C which is a neurotoxin.
Store-bought mushrooms are generally considered safe for dogs to eat. However, you should avoid feeding your dog any mushroom of unknown origin, especially if it is foraged.
Mushroom toxicity ranges from mild intestinal irritation and vomiting, diarrhea or abdominal discomfort to serious toxicity and death.
As a rule, don’t feed your dog mushrooms you wouldn’t eat. 
Star fruit (a.k.a. carambola)
Star fruit may be a great addition to your kid’s lunchbox, but sadly, not to your dog’s bowl.
It contains oxalates and caramboxin. Oxalates have already been discussed previously and cause calcium deficiency and kidney stones.
Bones are a common reason why dogs end up needing emergency surgery.
Bones, while being a good source of calcium, can splinter, and the sharp edges can cause intestinal perforation (especially when eaten alone) and severe infection.
Some greedy dogs sometimes swallow large chunks of bone causing an intestinal blockage which can lead to even more life-threatening complications.
Cooked bone is particularly prone to splintering and is best avoided. If you must give your dog a bone, give them a raw bone that is big and hard enough for them not to swallow whole or splinter. 
The Bottom Line
We hope that this list will give you a fair idea of what human food items dogs should not eat. It is best to always do your research about any new food item you intend to feed your dog.
Be careful of the information you find on the internet. People are free to write just about anything on the internet.
We, therefore, suggest that you talk to your trusted veterinarian before feeding anything new to your dog.