Two dogs are twice the fun for most pet parents. But when those pups are siblings adopted from the same litter, problems such as littermate syndrome can pose challenges to the puppies’ social development. Discover what littermate syndrome in dogs is, how to handle it, and the best way to welcome a new pup into your home. While you’re here check out our new puppy checklist and make sure you have everything you need for your new bundle of joy!

What exactly is “littermate syndrome” and is it real?

Littermate syndrome can occur when two puppies adopted from the same litter grow up together in the same home. In some cases, these sibling puppies form such a deep bond with each other that they fail to properly socialize with people and other dogs. When these two pups must be separated from each other even for a short time, they may whine, exhibit destructive behavior, bark excessively, or show extreme anxiety in new situations.

Raising two sibling puppies of the same age together (whether from the same or different litters) is a risk for developing littermate syndrome. Most experts agree that dog parents can avoid littermate syndrome by getting one puppy at a time then waiting a year or two to introduce second puppy to the family.

Littermate syndrome is not a medical diagnosis, but most experienced dog parents and veterinarians can attest that it is real.

One of the worst aspects of littermate syndrome is that your pups don’t properly bond with you. And isn’t that the whole reason you got a dog in the first place?

At what age does littermate syndrome start?

Puppies are typically ready to live away from their mom and siblings at around 8-12 weeks old. At this point, the pups begin their journey to an independent, confident doggie life.

If adopted siblings are kept exclusively together after 12 weeks of age, they may become each other’s “security blanket.” As a result, they miss out on a critical phase of social skill development, resulting in stunted socialization skills and anxiety when they are separated.

Is littermate syndrome common?

Because littermate syndrome is not an official diagnosis, there is no data to illustrate its prevalence. Raising two puppy siblings together does not guarantee that they will develop littermate syndrome, but it increases the odds of poor socialization. If you do decide to get two pups at the same time, it is possible to avoid littermate syndrome through consistent training and some hard work.

two back and white husky puppies playing with each other against a brick wall

What are the most common symptoms of littermate syndrome?

When two puppies are raised together beyond three months of age, they can become overly dependent on each other. The pups can become so deeply bonded that they live in their own little sphere of safety, separated from the outside world. The attention they give each other is so intense that they can fail to live independently or interact appropriately with other dogs or people.

Here are some of the most common symptoms of littermate syndrome:

Extreme co-dependence

When two pups experience littermate syndrome, they are so dependent on their sibling for security that they resist anything that takes them out of their comfort zone – meaning any new activity, person, dog, or location.

Separation anxiety

The result of this codependence can be separation anxiety that occurs whenever something causes the two puppies to be physically separated from each other. The pups can be so overwhelmed by the separation that they could have a complete meltdown. Something as simple as walking on separate leashes can be enough to trigger the pups’ anxiety.

Poor social skills

Even though your two pups are always socializing with each other, that doesn’t mean that they are good at socializing with anyone else. If the pups were raised exclusively together beyond three months of age, they were denied the opportunity interact with other dogs and humans during a critical phase of puppy development.

Even worse, your two puppies may not have equal status – one may be more dominant than the other, which can lead to aggression.


When two pups are codependent, they may focus so strongly on each other that they fail to interact with the people and things around them. They never develop the confidence that comes from exploring and learning about their surroundings. The result? A powerful fear of anything new, which sends them directly to their comfort zone with their sibling.

Read more: Expert Reveals Everything You Need To Know About Fear In Dogs

Training difficulties

Training your pup is essential to establishing good behavior and strengthening your bond with them. This training should begin as early as eight weeks old, or as soon as you bring your pup home for the first time.

Training just one puppy can be challenging even on a good day. With two pups experiencing littermate syndrome, dog training becomes exponentially harder. Why? Because your dogs are so co-dependent that that struggle to pay attention to anything else.

Sibling aggression

While not always present with littermate syndrome, aggression can arise when one puppy is more dominant than the other. The bullying by the dominant sibling can become more intense as the dogs grow.

puppies running through grass

What behaviors can be perceived as littermate syndrome symptoms?

The behaviors associated with littermate syndrome can appear in any dog or in any combination. It’s not always possible to pinpoint the cause of anxiety, aggression, or destructive behavior in a dog, even if it is being raised with a littermate.

Experts recommend viewing each of your dogs as an individual and addressing their behavior issues in a customized way. Blaming littermate syndrome for your dogs’ symptoms may cause you to miss other causes for their anxiety or aggression. Each situation, just like each dog, is unique.

Does littermate syndrome go away?

The short answer is no, littermate syndrome does not go away on its own. But the behavioral issues that arise from two sibling puppies being raised together can be addressed. It may take a significant amount of effort on your part to help your dogs achieve proper socialization skills and good behavior.

You’ve already adopted a pair of littermates?

Raising a pair of sibling puppies does not guarantee that they will develop littermate syndrome. If you’ve already adopted two pups, your first task should be helping each pup be comfortable without their sibling. This includes training, crating, and walking them separately. Yes, this is time consuming, but remember that your goal is to nurture each pup’s self-confidence and to build a strong bond of trust.

Should you consider rehoming one of your puppies?

Sometimes, the aggression that arises from littermate syndrome can lead to unsafe situations, especially for the less-dominant of the sibling puppies. Or, if the two littermates develop a pack mentality, they could team up to be aggressive toward other dogs or people, including you.

When your pets are aggressive, they are not happy, playful, or relaxed, and neither are you. Address aggressive behaviors as soon as they appear. Your veterinarian or a professional trainer can be a great resource.

If you’ve tried everything possible and nothing is reducing the aggression, it may be time to consider rehoming one of your pups. Your dogs and your family deserve to live in a safe and peaceful environment.

Will getting a third dog help with littermate syndrome?

Some say that having a third dog – not a puppy, but an older dog – can help avoid littermate syndrome. In theory, the sibling puppies bond with the older dog as well as each other, which helps them develop better social skills. There is no solid evidence to back up this claim, and of course each situation is unique.

How to fix littermate syndrome

Overcoming the behavioral issues associated with littermate syndrome is a huge task. If you want your dogs to ultimately become confident when separated from each other and disciplined when they are together, be prepared to invest the time and energy to reach these goals. It will be worth it, we promise!

Address their separation anxiety

The first step in fixing littermate syndrome is to help your sibling puppies get used to being apart from each other. Without this important step, you can’t help each dog individually without one or both of them experiencing a meltdown.

Easing your pups’ separation anxiety is a slow process of desensitizing them to being away from their sibling. Simply placing them in separate rooms and closing the doors won’t solve the problem. This will just create more separation anxiety.

  1. Start by buying two crates of the proper size. Place each puppy in a separate crate, but keep the crates right next to each other, allowing the puppies to see, smell, hear, and touch each other.
  2. Over the next few weeks, move the crates farther away from each other. Always make sure the puppies can still see each other. Eventually, the puppies should be able to remain calm while on opposite ends of the same room.
  3. Once the puppies can remain calm for 30 to 60 minutes in their separate crates, try moving them out of sight of each other. You can leave them in the same room, but slide a box or chair between the crates so they can’t make visual contact with each other.

During this process, keep a close eye on the pups. If they become overly anxious, whine constantly, or bark constantly, go back a few steps in the process.

One key to success is offering high-value enrichment to each pup while they are separated from each other. Give them a frozen treat or favorite toy. This will help the pups to equate alone time with positive experiences. They may even begin to look forward to being separated!

woman in green sweater holding small brown dog with cages in the background

Consider training them separately

Once your dogs are OK with being apart from one another, you can begin training them separately. Dog training sessions take a lot of concentration and to make these sessions successful, your dog must be completely focused on you. Having their sibling present or even in the same room can be too distracting completely disrupt your dog training session.

Obedience training is not a quick process. Be prepared to spend months, if not a year, working on this process. Not only will these training sessions help your dogs learn confidence and independence, you’ll build a bond of trust with each pup.

Build their independent behavior

Now that each puppy can be away from their sibling and has their training basics down pat, you can reinforce their independence by treating each pup as a separate dog rather than as a single unit. Feed them separately, take them on separate walks, play with them separately, and take them to the vet one at a time.

Get them back together

During this process, your dogs will of course see each other and spend time together. But only after they have mastered the art of being relaxed and happy when apart from their sibling should you consider taking them to the park together or training them together.

Avoid littermate syndrome by getting one puppy at a time

Your life is busy enough without having to help two puppies overcome serious, long-lasting behavioral issues. Rather than get two puppies at the same time, get just one pup, then adopt another puppy a year or two later. This way, you can focus on raising confident, independent dogs and building a solid bond with each of them.