Do Dogs Throw Up When On Heat? (Vet Answer)

Dr Daisy May, MRCVS BVSc, Vet Surgeon
Do Dogs Throw Up When On Heat

Being ‘on heat’ is a common colloquial term for the period of your female dog’s reproductive cycle that is scientifically termed ‘estrus’. During the estrus period, your dog is able to become pregnant, whereas the rest of the time, mating will not result in pregnancy.

As a vet, it is not uncommon for pet owners to ask me in the consulting room whether throwing up might be an expected consequence of their female dog being on heat.

And indeed, as a human female (with many human female friends), I can vouch for the fact that nausea can occur due to regular, cyclical fluctuations in our reproductive hormones!

The truth is that while nausea (resulting in loss of appetite) and vomiting may be linked to similar reproductive hormone fluctuations in our canine family members during heat, far more often throwing up is nothing to do with the fact that your dog is on heat!

dog sleeping

Why Do Female Dogs Throw Up?

As a general rule, if your dog throws up more than once in a 24-hour period, is lethargic, off their food, or appears otherwise unwell, then you need to see a vet without delay.

In fact, statistically, it is much more likely that the vomiting has some other cause, and the timing of your furbaby being on heat is merely an unrelated coincidence. By far, the most common cause of vomiting seen at vets’ practices on a daily and weekly basis is ‘dietary indiscretion’, that is, your dog has ingested something they really shouldn’t have!

Whether this has occurred at the hands of a well-meaning but misguided human or whether your pooch took it upon herself to plan her own menu using the kitchen bin as a drive-by diner.

If your pet is vomiting, the first question to ask yourself is whether they have (or could have) eaten anything out of the ordinary over the last 24 hours. If the answer is yes, then this is probably the cause of the problem!

Other non-estrus-related causes of vomiting in dogs include food sensitivity or allergy; infections such as giardia or salmonellosis; liver or kidney disease; endocrine diseases such as hypothyroidism or Addison’s disease; or many other conditions which require veterinary examination and diagnostics to confirm.

Consider too, that if your dog likes to chew on (or even tries to swallow) non-food items such as toys, stones, or socks, then you also need to decide whether this could be a possibility.

Swallowing a non-food item that then becomes stuck in the stomach or intestines is a potentially very dangerous cause of vomiting in dogs, requiring prompt veterinary attention.

How To Identify If Your Dog Is On Heat

A further important diagnostic question is whether you are sure your dog is on heat. The majority of female dogs will experience estrus about every six months, that is, twice yearly. But there are definitely exceptions to this rule!

For some individuals (especially smaller breeds), having three heats per year can be normal. And in some cases (particularly large or giant breed dogs) the female may only have one estrus period every twelve months. Again, for lots of individuals, this is normal!

Usually, the first sign of heat that will be noticed is swelling of the vulva (external genitals), but this is not always particularly obvious. A bloody vaginal discharge quickly follows, and is more likely to be noticed, especially (unfortunately) on the couch and the beds! Some female dogs produce a fairly large amount of vaginal discharge when on heat, and others produce very little.

After a few days, the vaginal discharge will become thinner, more watery, and change color from reddish brown to pinkish, before eventually stopping entirely. The estrus period lasts for 10-14 days on average. 

Photo by Dominika Roseclay on

What To Do When Your Dog Is Throwing Up

So, if you have a vomiting dog on your hands, try to establish whether your dog is on heat. Consider when they were last in season; if it has been significantly longer or shorter than six months, there is a greater chance that it is not in fact heat but perhaps a uterine infection requiring medical intervention.

Pyometra is a life-threatening uterine infection that can masquerade as heat, and you should be especially vigilant for this condition if your furbaby is also throwing up. Pyometra typically occurs 2-8 weeks after heat, and common signs to look out for include vomiting, loss of appetite, drinking more water than usual, and licking the vulva more frequently.

If your dog has developed pyometra, you might notice a bloody or purulent (white, yellow, or green) discharge from the vulva, which may have an unpleasant smell.

Making things even harder, some dogs with pyometra will not produce any vaginal discharge at all, due to their cervix being closed. This can make the condition harder to diagnose, requiring a digital vaginal examination and ultrasound scan at the vet clinic.

Treatment of pyometra may be medical or (ideally) surgical and must be undertaken promptly to ensure the best possible likelihood of a good outcome for the patient.

Phantom pregnancy is the second condition that can masquerade as heat and cause vomiting in female dogs. This condition occurs 6-8 weeks after the heat and is a hormonal disorder that effectively ‘tricks’ your dog’s body into believing that it is pregnant.

During a phantom pregnancy, the mammary glands become more developed (larger and more obvious), and the vulva may be swollen (hence the appearance of being in heat).

Your dog will likely also exhibit behavioral changes including nesting behavior, clinginess, and in some cases becoming protective or even aggressively guarding one or more favorite toys (which she now considers to be her ‘puppies’!)

The persistently high level of progesterone a dog experiences during a phantom pregnancy can cause a morning-sickness-like syndrome, and your pooch may go off her food, or even throw up.

Treatment of phantom pregnancy involves giving oral medication prescribed by your vet once daily for several days. Your dog is extremely likely to go on to have further phantom pregnancies after every subsequent season, and because repeated phantom pregnancies increase the risk of pyometra, spaying these dogs is highly advisable.

Wrapping Up

Heat (or estrus) is the stage of your dog’s reproductive cycle where she can become pregnant if mated. On average, it lasts 1 ½ to 2 weeks, and most dogs come into heat around once every six months.

Normal signs of heat include bloody (red, brown, or pink) vaginal discharge, a swollen vulva, and an increased interest in male dogs. Female dogs can throw up as a consequence of the reproductive hormone fluctuations that occur during the heat.

In this instance, no treatment may be required. However, it is far more likely that your dog is vomiting for some other, non-related reason!

The most common cause of vomiting in dogs is dietary indiscretion. Vomiting and signs are similar to those of being in heat can also indicate pyometra or phantom pregnancy, both of which require veterinary intervention.

If your dog might have eaten a non-food item, or you believe there is a chance she could have developed a pyometra, then you need to book an emergency, same-day vet appointment.

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