He no longer plays. He eats less. He lies awake for a long time, not really participating in what is happening around him. He no longer greets his owner, seeks less contact, seems to have lost the drive, the joy of life he once had.

Many owners then say their dog is "depressed." The word is understandable because it accurately describes what is observed: a subdued dog, less lively, less engaged. But from a scientific standpoint, more precision is needed.

In dogs, a diagnosis of depression in the strict human psychiatric sense cannot be made. This diagnosis is partly based on what the person feels and can verbalize: persistent sadness, loss of pleasure, dark thoughts, feelings of guilt, inner experience. A dog cannot describe these things to us with words.

This does not mean that the subject does not exist.

Research in dogs studies states analogous to certain aspects of depression, often called "depression-like" states. These states are approached based on observable signs: withdrawal, loss of interest, decreased activity, reduced responsiveness, changes in usual behaviors, but also based on cognitive and biological models.

Therefore, one cannot simply say, "my dog is depressed" as one would for a human. But neither can one dismiss a dog that is losing its vitality by saying "it will pass." Between the two, there is a more accurate approach: observe, look for possible causes, check the medical status, then adapt the care.

What science establishes

The historical starting point is the learned helplessness model. The work of Seligman and Maier showed that an animal exposed to uncontrollable aversive events can eventually become less likely to try to escape the situation, even when an escape becomes possible.

Aversive event: In behavioral science, an aversive event is a situation or stimulus that the animal seeks to avoid, flee from, or stop because it is perceived as unpleasant, stressful, painful, or threatening. In the context of learned helplessness, "uncontrollable aversive events" therefore refer to negative experiences over which the animal has no control.

Neuroscientific reinterpretation of this model shows that this passivity is not simply a "bad habit," but involves brain circuits related to stress, control, and adaptation.

This model does not prove that dogs experience human depression. However, it does show that a sustained state of withdrawal after exposure to uncontrollable situations is biologically plausible in this species.

In companion dogs, recent research has particularly focused on prolonged waking inactivity. This refers to a dog that is not sleeping but remains inactive for a long time, with little engagement in its environment. The study by Harvey and colleagues, published in 2019, explored this avenue in shelter dogs. The authors showed that this behavior could be measured and associated with certain negative evaluations by observers. However, their conclusions remained cautious: the results did not clearly confirm the existence of a depression-like syndrome.

The follow-up study published in 2020 further reinforced this caution. It did not confirm the expected association between greater waking inactivity and a more pessimistic judgment bias. In short, the idea was interesting, but waking inactivity alone is not enough to demonstrate a depression-like state in dogs.

This point is important. A dog that remains lying down, awake and inactive, could be in pain, tired, sick, elderly, anxious, under-stimulated, recovering, or simply in a poor environment. Inactivity is a serious signal to be considered, not a diagnosis.

The most rigorous formulation is therefore: science does not validate a direct equivalence between "canine depression" and human depression.

However, it does acknowledge the possible existence of sustained states of withdrawal, loss of interest, and emotional suffering in dogs, which may share certain mechanisms with depressive models studied in other mammals.

Biological mechanisms

The hypothesis of depression-like states in dogs is credible because it is based on biological mechanisms widely shared among mammals.

Learned helplessness shows that an animal can lose its ability to act when it learns that its actions do not change what happens to it. In Maier and Seligman's modern work, perceived control over the environment plays a central role: what protects the animal is not the complete absence of difficulty, but the ability to have some agency over its experiences.

In dogs, this relates to very concrete situations: lack of choice, unpredictable environment, repeated stress, isolation, lack of stimulation, inability to avoid certain manipulations or constraints. These factors do not automatically cause a depression-like state, but they can contribute to a state of disengagement in certain individuals.

Another tool used in research is judgment bias. The principle is to observe how an animal responds to an ambiguous situation. An animal in a more positive emotional state will tend to respond more "optimistically," while an animal in a more negative state will more often respond "pessimistically." The systematic review and meta-analysis by Lagisz and collaborators showed, across many species, that affective and environmental conditions indeed influence these responses. This is not a test for depression, but it is a useful tool for approaching the emotional state of a non-human animal.

Anhedonia is also an important concept. It refers to the loss of interest or pleasure in normally motivating activities. In humans, it is one of the major signs of depression. In animals, it is mainly studied in experimental models, particularly in rodents exposed to chronic stress. These models cannot be directly transposed to companion dogs, but they help to understand why a sustained loss of interest in play, exploration, food, or social interactions should be taken seriously.

Grief and social loss

The loss of a companion, another animal in the household, or a close person can lead to sometimes significant behavioral changes in certain dogs. A decrease in activity, reduced play, changes in appetite, increased seeking of contact or, conversely, social withdrawal have been described after the loss of a companion.

A study published in 2022 showed that many owners reported these types of changes after the death of another dog living in the household. The authors refer to behaviors related to social loss, while remaining cautious about the exact emotional interpretation of these reactions.

It is therefore reasonable to consider that a dog can be affected by the disappearance of an individual to whom it was strongly attached. However, it is more rigorous to speak of distress related to social loss or grieving behaviors than to state that it experiences exactly the same grief as a human.

When these changes persist for several weeks, are accompanied by significant loss of appetite, marked withdrawal, or a general decline in health, a veterinary consultation is recommended.

What it means in practice

In everyday life, certain changes should raise a red flag.

A dog may lose interest in walks, games, food, social interactions, or activities it previously enjoyed. It may become more passive, less curious, less responsive. It may remain motionless for long periods while awake, no longer seek contact, no longer follow usual routines, or seem "subdued."

These signs do not prove depression. They primarily indicate that a significant change is occurring.

Comparison with the dog's usual behavior is essential. A naturally calm dog that sleeps a lot but eats well, interacts normally, and maintains its habits is not the same as a dog that was previously cheerful, playful, and sociable but suddenly becomes withdrawn, isolated, and disinterested.

This type of presentation can appear after social loss, abandonment, a sudden change of environment, hospitalization, a period of pain, decreased activity, trauma, or a significant disruption of routine.

Recent work also suggests that some dogs may show behavioral changes after the death of a close companion: decreased play, decreased activity, attention-seeking, changes in appetite, or increased vocalizations. The authors describe these as behaviors related to grief, while remaining cautious about the exact interpretation of what the dog feels.

This is an important nuance. Saying that a dog can be affected by the loss of a companion is consistent with available data. Saying that it experiences grief exactly like a human would be too assertive.

What is misunderstood or misinterpreted

The first error is to say that dogs cannot be affected because they do not have human consciousness. This reasoning is too reductionist. Animal behavior science does not require an animal to speak to study its state. It relies on what can be observed: behavior, cognition, physiology, stress response, adaptability.

The second error is to call any calm, tired, or unexpressive dog "depressed." A quiet dog is not necessarily suffering. An older dog that slows down is not automatically depressed. A dog that sleeps a lot after an intense period may simply be recovering.

The third error is to trivialize a lasting change. A dog that no longer plays, eats less, isolates itself, loses interest in interactions, or does not return to its usual level for several weeks should be evaluated. Even if it's not "depression," it's not a minor detail.

The fourth error is to psychologize too quickly. In dogs, chronic pain, endocrine disorders, systemic diseases, neurological disorders, loss of vision or hearing, the effects of age, or cognitive dysfunction syndrome can give an impression of sadness, sluggishness, or withdrawal.

Finally, psychotropic treatments should not be caricatured. In veterinary behavioral medicine, certain molecules acting on serotonergic systems or related pathways are used for specific indications: anxiety, compulsive behaviors, stress-related disorders, certain severe behavioral disorders. The Merck Veterinary Manual notably mentions the veterinary use of several classes of psychotropics, including tricyclic antidepressants and selective serotonin reuptake inhibitors, in regulated contexts.

This does not mean that all sad or calm dogs should be medicated. It means that, in some cases, medication prescribed by a veterinarian can be part of a serious care plan. Self-medication is, of course, to be avoided.

Which dogs require particular vigilance?

Certain dogs deserve special attention.

This is the case for dogs who have experienced significant social loss, abandonment, abuse, a sudden change of home, hospitalization, a period of pain, or a sudden transition from a life rich in activities to a life much poorer in stimulation.

Older dogs should also be closely monitored. In them, a gradual withdrawal can be linked to pain, arthritis, sensory loss, a general illness, or cognitive dysfunction syndrome. From the outside, this can resemble "depression," whereas the primary cause is medical.

Very active dogs or those strongly attached to a routine may also struggle with a sudden drop in activity: cessation of sports, convalescence, changes in household rhythm, moving, loss of a companion, arrival of a new animal, or significant modification of their relationship with their owner.

Before attributing a state of withdrawal to an emotional cause, it is therefore necessary to check for major competing medical causes: pain, endocrine disorders, inflammatory or systemic diseases, neurological disorders, sensory deficits, medication side effects, pathological aging.

In dogs, the most costly error is often to too quickly conclude a "mental" problem, when the body is already sending signals.

Can a dog exhibiting a depression-like state be helped?

When a dog shows a sustained loss of interest in its environment, decreased activity, social withdrawal, or a reduction in its usual behaviors, management primarily depends on the underlying cause.

The first step is to investigate a medical origin. Chronic pain, general illness, an endocrine disorder, neurological damage, or cognitive dysfunction syndrome can produce a picture very similar to what is sometimes interpreted as depression.

Once medical causes are ruled out or managed, several approaches can be considered:

• environmental improvement and enrichment;
• restoration of predictable routines;
• gradual reintroduction of enjoyable activities;
• increased social interactions adapted to the dog;
• reduction of sources of chronic stress;
• individualized behavioral work.

In some situations, particularly when withdrawal is significant or associated with severe anxiety, medication may also be prescribed by a veterinarian. Medications used in behavioral medicine are not intended to "make the dog happy" but to restore emotional functioning compatible with behavioral work and an improved quality of life.

Progress is often gradual. As in humans, a return to normal functioning generally does not occur in a few days.

When to consult

Veterinary advice is necessary if the loss of enthusiasm, withdrawal, decreased appetite, unusual inactivity, or deviation from usual behavior persists for more than two to three weeks.

A consultation should be sought more quickly if the change is sudden, intense, worsening, accompanied by weight loss, visible pain, limping, digestive problems, a significant decrease in appetite, marked isolation, or a clear change in sleep patterns.

The first step must be medical. It is essential to look for pain, illness, hormonal disorders, neurological damage, sensory deficits, or age-related problems.

If no sufficient organic cause is found, behavioral management can then be implemented. This may include environmental adaptation, a gradual return to motivating activities, more targeted enrichment, a more predictable routine, work on the relationship, reduction of stress sources, and sometimes treatment prescribed by a veterinarian.

There is no magic recipe. A dog that is losing its vitality needs a serious assessment of its condition, not a quick interpretation or a promise of an immediate solution.

________________________________________________________________Sources 

1. Maier SF, Seligman MEP. Learned helplessness at fifty: Insights from neuroscience. Psychological Review. 2016.
2. Harvey ND, Moesta A, Kappel S, Wongsaengchan C, Harris H, Craigon PJ, Fureix C. Could greater time spent displaying waking inactivity in the home environment be a marker for a depression-like state in the domestic dog? Animals. 2019.
3. Harvey ND, Moesta A, Kappel S, Wongsaengchan C, Harris H, Craigon PJ, Fureix C. Investigating putative depression-like states in the domestic dog: does greater time spent displaying waking inactivity in the home kennel co-vary with negative judgment of ambiguity? 2020.
4. Lagisz M et al. Optimism, pessimism and judgement bias in animals: A systematic review and meta-analysis. Neuroscience & Biobehavioral Reviews. 2020.
5. Uccheddu S, Pierantoni L, Albertini M, Pirrone F. Domestic dogs may show grief-related behavioural and emotional patterns after the loss of a companion dog. Scientific Reports. 2022.
6. Merck Veterinary Manual. Psychotropic agents for treatment of animals.