Dogs who may normally be friendly with other dogs can sometimes become reactive and aggressive when attached to a leash. This behavioral trait, known as leash aggression or leash reactivity, is most frequently triggered by fear or frustration, although a high prey drive can lead to aggression when leashed as well.

Reactivity and aggressive behavior when on the leash is fairly easy to extinguish compared to more generalized aggressive behaviors, but in some cases, the dog requires additional medical support in the form of psychiatric medications.

Normally friendly dogs may become more aggressive when on the end of a leash, a behavior known more commonly as leash reactivity or leash aggression.

Leash aggression in dogs can occur rather suddenly, particularly as it becomes more ingrained, but in many cases, the animal may show signs of anxiety or fear prior to the lunging and barking that is characteristic of this condition. Some of the signs a dog is feeling anxious may include:

Fear driven leash aggression is usually focused on other dogs or on humans. Fast moving vehicles such as bicycles, skateboards, and even cars can incite an aggressive fear response from an animal that isn’t familiar with these items. 

In some situations, the aggression starts as curiosity and excitement, then changes to aggression when the dog is held back from its goal. The animal may also experience pain when attempting to reach the object of their interest, which can cause them to begin associating the item with pain and frustration instead of curiosity.

Some dogs pull and lunge on their leashes when they see a prey animal such as a squirrel or rabbit. Although treats are frequently successful in extinguishing the aggressive behaviors for fear and frustration, they tend to be less effective when the aggression is related to a high prey drive.

Dogs can develop problems with leash aggression and reactivity for several reasons. One of the most common reasons has to do with the nature of the leash itself. A dog that is trying to reach something interesting and instead is held back by the leash it both frustrates their ability to investigate and frequently causes pain as well. Dogs that are properly trained for loose lead walking are less likely to develop aggression when walking on the leash. 

If the dog is afraid of other dogs or of people, the inability to utilize the option of flight may cause them to choose fight instead, leading to aggression towards the object of fear. Occasionally the aggression is triggered or exacerbated by illness or injury making the dog feel vulnerable and afraid.

If your veterinarian suspects that there is a medical component to the behavior at all they will start the visit by performing a complete physical examination, which typically includes standard diagnostic tests such as a biochemistry profile, a complete blood count, and a urinalysis. Additionally, tests to check hormone levels may be recommended as imbalances thyroid hormones can increase overall aggression. 

A behavioral history will generally be collected at this time for any aggression related disorders. This history will usually include as much information as possible regarding the patient’s sex, age, and parentage as well as any available knowledge about the dog’s behavior when not on a leash and any physical or emotional traumas they have experienced in the past. Information surrounding the episodes of aggression will also help the veterinarian or behaviorist to craft the behavioral training program and may help to decide if psychiatric medications would be beneficial for the specific circumstances.

Treatment for aggression issues like leash reactivity will depend on both the severity of the reactions and the underlying trigger for the behavior. Fear reactivity on or off leash can be a potentially dangerous situation and should be addressed by with a veterinary professional’s guidance. Treatment for dogs who have shown any form of aggression should be a cooperative effort between a professional trainer or behaviorist and the owner of the animal. Scolding or physical correction is counterproductive with attempting to manage leash reactive behavior as it may enforce their feelings or fear and frustration and increase the chances that the initial reactivity turns into aggressive behavior. 

One of the more commonly employed training methods to mitigate aggression disorders is known as desensitization, a method in which positive stimuli such as treats and praise are used in conjunction with the presence of the object that the animal is reacting to so that the objects a become more a more positive and familiar presence and thereby reduce the aggression associated with it. Another training method, known as counter-conditioning may be utilized to distract the dog from negative stimuli. In some situations, behavioral therapy and training are sufficient to calm the dog, and either anti-anxiety or antidepressant medications may be employed to ease your companion’s discomfort.

Behavioral conditions related to aggression, whether on leash or off, often require lifelong behavioral management and training, sometimes combined with psychiatric medications. Medications that are administered for psychological imbalances frequently require several weeks before they become fully effective, and it is essential that your veterinarian knows all of the other medications being administered to your dog.

The way that canines metabolize these types of medications is very different from the way that a human metabolizes the drugs and dosages will vary based on your dog’s specific response to the medication. Medications alone are rarely effective in eliminating aggression-related behaviors, and continuing behavioral training and management will be needed to help your pet to become a happier and healthier individual.