Overdose

• An overdose may occur if you give your dog an excessively large dose. According to Pet Place, "This may be due to each member of the family medicating the pet without knowing that he has already received his medication, the curious pet chewing the bottle and ingesting all the medication or in certain situations even when the pet is on the proper dose."
  
  

Symptoms

• Certain medications, such as heartworm medication, may cause vomiting, diarrhea or lack of coordination. This can occur if you give the dog more than the recommended dosage.
  
  

Over the Counter

• Some forms of medication can be given to dogs without a prescription, such as aspirin. Too much aspirin or other over-the-counter medications may cause an upset stomach.
  
  

Complications

• Sometimes dogs will suddenly stop needing the medication they have been taking for a period of time.This can result in other complications. Pet Place notes, "A good example of this situation is diabetes. Pets may require a specific dose of insulin and do well on that dose for quite a while. Suddenly, the dose you are giving may be an overdose and the pet becomes hypoglycemic."
  
  

Small vs. Large Breeds

• Small dogs usually require less medication than large dogs. Consult your veterinarian if you are unsure of dosage requirements.