Dog owners love to treat their pets every once in a while, but it can be hard to know what's safe for your four-legged family members to eat. This list includes 21 common household foods and small objects that pets should avoid eating at all costs.

And if you're a cat owner, check out our companion list of things they shouldn't eat.

If your pet has eaten something dangerous, contact your vet right away or phone the Pet Poison Helpline at 855-764-7661 (there is a fee for calling).

1. Chocolate

Most people know about the risk of feeding dog chocolate, but we could all use a reminder. The dangerous ingredient of chocolate is theobromine, which gives it a bitter taste. That means darker chocolate is especially dangerous for your pet.

It will usually take a few hours for your dog to show symptoms, including vomiting, diarrhea, restlessness, hyperactivity, and sometimes seizures. While a very small amount of chocolate is nothing to worry about, you should be cautious not to leave any lying around.

2. Milk

Like some humans, dogs are essentially lactose intolerant. Their stomachs have trouble digesting milk and other dairy products. The worst you can expect is some diarrhea or an upset stomach, but it's best not to treat your dog to milk.

3. Allium Plants

Most pet owners have no ideas, but this family of flowering plants which includes onions, garlic, and chives is very dangerous for dogs. They irritate your pet's gut and can cause conditions like anemia.

Watch out, because some surprising products, including gravies and baby foods, contain garlic.

4. Bones

The "bones" we buy for dogs at the pet store are actually made from pressed animal hides. Real bones can damage your dog's teeth (they're used to chewing on kibble, not hunting wild animals). Beware of cooked bones too, because these will splinter easily and become a choking hazard.

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5. Xylitol

You may not recognize this artificial sweetener, but you probably have it in your home right now. Diet sodas, sugar-free gum and some candies all use xylitol. Just a small amount can be fatal for dogs, because the sweetener causes blood sugar and liver problems.

6. Macadamia Nuts

Some nuts such as peanuts,  nuts are actually a nice treat for your dog, but leave macadamia nuts out of the mix. They can wreak havoc on a dog's digestive system. They may also cause tremors, weakness, vomiting, and overheating. Be aware that the symptoms are often delayed, but can last for a long time.

7. Pest Control Products

Treat chemicals in your home as if you're living with a toddler: make sure they're out of your dog's reach and properly sealed. Common insecticides are toxic to dogs, especially disulfoton, which is used on roses.

Obviously, you shouldn't let your pet drink rodenticides either, but also don't let them eat any rodents you've poisoned using those chemicals.

8.  Veterinary Pain Relievers

This can seem like strange advice since they're prescribed by a veterinarian, but pet pain relievers are only safe in very low doses. Giving your pet large doses of Rimadyl, Dermaxx, Previcox or COX-2 inhibitors can cause ulcers and kidney failure.

9. Household Cleaners

Even if the label insists that these products are "natural," be careful about using them on surfaces that your dog can reach. The most dangerous products are lye, drain and toilet cleaners, and calcium, lime and rust treatments.

10. Blue Cheese

Cheese is alright as a "sometimes treat" for your pet, but only certain kinds. Blue cheese varieties like Stilton and Roquefort contain a chemical called Roquefortine C, which causes vomiting, diarrhea, tremors and even seizures in dogs.

Keep reading, because lots of common ingredients aren't safe for your dog to eat...

11. Caffeine

It probably won't hurt your dog to lap up a few drops of coffee. Still, caffeine affects your dog's tiny body very seriously, raising their heart rate dangerously high and impacting their nervous system. Some caffeine beverages also contain theobromine (the chemical from chocolate) and sweeteners like xylitol, so don't share your drink with Fido.

You also need to make sure that caffeine products like tea bags and coffee pods are properly disposed, or else your pet might snack on them.

12. Corn On The Cob

As a rule, vegetables are healthy and safe treats for your dog. But corn is an exception. It simply does not digest well in your pet's stomach, and can make their whole system "backed up." Look for signs that your dog is suffering from constipation, including lack of appetite and restlessness.

13. Alcohol

Your dog will probably vomit up any alcohol they drink, but it's important to know about the effects it can have on them. Even a small amount of liquor has a strong effect on dogs because of their size. Drinks can cause vomiting, diarrhea, dizziness, or a coma and death in more serious cases.

14. Yeast Dough

Bread and pastries are unhealthy but a safe snack for dogs in small quantities. But the raw yeast dough is very dangerous. As the yeast rises, gas is released into your dog's digestive system.

It sounds silly, but this gas can be painful for your dog and block their intestines, causing constipation.

15. Raisins and Grapes

Like allium plants, dogs cannot digest raisins and grapes. They are toxic to your dog, and even a small amount can be fatal because they cause severe kidney damage. Look out for vomiting and diarrhea, as well as a loss of appetite, bad breath, ulcers in your dog's mouth, and lack of urine.

In serious cases eating grapes or raisins can put your dog into a coma.

16. Moldy Foods

Of course, you wouldn't feed your pet moldy kibble, but you probably wouldn't be too worried if they were eating out of your trash can either. In fact, the toxins in moldy food scraps can have a variety of effects - all bad - on your dog's health. So secure the lid on the garbage can in your kitchen.

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

Like other products meant for humans, the effects of these common household medicines are much stronger when dogs swallow them. If your dog gets into a bottle of Aspirin or Motrin they could suffer from kidney failure and stomach ulcers.

18. Amphetamines

Drugs used to treat ADD or ADHD are not safe for dogs. Medicines like Adderall and Concerta can cause tremors, seizures, overheating and heart problems in dogs.

19. Antidepressants

In America, the largest number of calls to the Pet Poison Helpline come after dogs eat antidepressants. They can cause sedation, seizures and lack of coordination in pets.

20. Fertilizers

It seems strange, but many types of fertilizer feature blood meal, bone meal, and feather meal, which may make them attractive to your dog. But keep them away from these products, because they tend to form a block in your dog's stomach, and this can be fatal.

21. Acetaminophen drugs

Tylenol and cough medicines are safe for humans, but not pets. If your dog has been looking for snacks in the medicine cabinet you'll notice they have severely dry eyes. Eating too many of these pills can cause liver damage, so leave the cap on.

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