Drontal for Dogs Side Effects: What to Watch For
By Dr. Zubair Khalid, DVM, MS, PhD ·
Most dogs take Drontal without any trouble, and the side effects that do show up are usually mild and short lived. Vomiting, drooling, and a day of low energy are the reactions owners report most often. A small number of dogs develop neurologic signs such as wobbliness or tremors, and those need a veterinarian right away.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- Mild vomiting, drooling, and lethargy are the most likely reactions, and they usually settle within a day.
- Give the tablet with a small meal unless your veterinarian says otherwise, since that can reduce stomach upset.
- Watch your dog for the first few hours after the dose, especially if this is the first time you have used the product.
- Call your veterinarian the same day if vomiting will not stop, if your dog seems unsteady, or if you see tremors or twitching.
- Never give a second dose to "make up" for one that came back up unless your veterinarian tells you to.
What Drontal Is and What Veterinarians Use It For
Drontal is an oral deworming product for dogs. It combines three active ingredients: febantel, pyrantel embonate, and praziquantel [1]. That combination targets the common intestinal worms veterinarians find in dogs, including roundworms, hookworms, whipworms, and tapeworms.
Veterinarians reach for it in a few situations. Puppies get dewormed on a schedule because they can pick up roundworms from their mother. Adult dogs get treated when a fecal test shows worm eggs, or when a dog has risk factors such as hunting, kennel life, or eating things they should not. In one field study of hunting dogs in southern Italy, a single treatment with Drontal Tasty reduced intestinal worm infections in naturally infected dogs [1]. Hunting dogs and rural dogs tend to carry a higher worm burden than pets who stay in the yard, which is why regular deworming matters for them [1].
Drontal is a treatment, not a monthly preventive for every parasite. Your veterinarian will tell you how often your dog needs it based on lifestyle, age, and fecal test results.
How Drontal Works
Each ingredient attacks worms in a different way, which is why the combination covers so many species.
Praziquantel damages the outer layer of tapeworms so they lose their grip and are passed out. Pyrantel embonate paralyzes roundworms and hookworms by blocking the nerve signals they use to move. Febantel works on whipworms and other worms by disrupting their energy metabolism. Because the drugs act on the worm and not on your dog's own nervous system at normal doses, most dogs do not notice much beyond a possible upset stomach.
The worms are not killed instantly inside your dog. They are expelled in the stool over the following hours to days. You may see worm segments or whole worms in the poop after treatment. That is expected and not a sign that the medicine failed.
If your dog also takes medication for anxiety or behavior, the same general rule applies: tell your veterinarian about every drug and supplement your dog receives before adding a dewormer. You can read more about what to watch for with those products in Dog Anxiety Medication Side Effects: What to Watch For.
Dosing Basics
Your veterinarian decides the dose. Drontal is dosed by body weight, and the right amount for a 12 pound terrier is very different from the right amount for a 90 pound retriever. Do not split a tablet based on guesswork or copy a dose from another dog.
Give the tablet as directed. Many owners hide it in a small amount of food or give it right after a meal to soften stomach upset. If your dog spits it out, offer it again in something tastier, but do not stack extra doses.
If you miss a dose, give it when you remember, unless it is almost time for the next one. In that case, skip the missed dose and go back to your normal schedule. Do not double up.
If your dog vomits within a couple of hours of the dose, call your veterinarian before repeating it. You do not know how much of the tablet was absorbed, and a second full dose could be too much.
Drontal for Dogs Side Effects: Common and Serious
Most reactions are mild and pass quickly. The table below separates the everyday ones from the ones that need a phone call or a trip to the clinic.
| Side effect | How common or serious | What to do |
|---|---|---|
| Vomiting | Common and usually mild | Withhold food for a few hours, offer small amounts of water, and call your vet if it continues past a day |
| Drooling or lip smacking | Common and usually mild | This often means the tablet tasted bitter. Offer water and a small treat |
| Lethargy or sleepiness | Common and usually mild | Let your dog rest. Call if it lasts more than 24 hours or your dog will not eat |
| Diarrhea or soft stool | Common and usually mild | Keep water available. Call if there is blood or if it lasts more than two days |
| Loss of appetite | Less common | Offer bland food. Call if your dog refuses food for more than a day |
| Wobbliness, tremors, or twitching | Rare but serious | Call your veterinarian or a poison control hotline right away |
| Seizure | Rare but serious | This is an emergency. Go to the nearest veterinary hospital now |
| Swelling of the face, hives, trouble breathing | Rare but serious | This is an emergency. Go to the nearest veterinary hospital now |
The neurologic signs are the ones owners miss. A dog who is a little sleepy after a dewormer is not the same as a dog who is unsteady on their feet, holding their head oddly, or having muscle twitches. Those signs point to a reaction that needs treatment, not watching at home.
Dogs with facial nerve problems can also show eye changes, including reduced tear production and corneal ulcers, and those signs can be mistaken for general sluggishness after medication [2]. If your dog's face looks uneven or one eye seems irritated, that deserves a veterinary exam. It is not a typical Drontal reaction, but it is easy to confuse with one.
Other dewormers and parasite preventives have their own side effect profiles. If you are comparing products, What Are the Side Effects of Bravecto for Dogs? What to Watch For covers a different class of drug. Antibiotics are another common source of stomach upset and appetite changes, and you can read about those in What Are the Side Effects of Antibiotics in Dogs?.
Who Should Not Take Drontal and What Interacts With It
Tell your veterinarian your dog's full history before the dose. Certain dogs need a different plan or a lower dose.
Dogs who should be evaluated carefully first include:
- Puppies under the age when the product is labeled for use
- Dogs who are pregnant or nursing
- Dogs with liver or kidney disease
- Dogs who have had a reaction to a dewormer before
- Dogs taking other medications, especially ones that affect the nervous system
Drug interactions matter. Products that contain pyrantel, praziquantel, or similar deworming drugs can overlap with Drontal, and doubling up on the same class of drug raises the risk of side effects. If your dog is on a monthly heartworm preventive, a flea and tick product, or a combination parasite tablet, your veterinarian needs to know before prescribing Drontal.
Combination parasite products are common in the United States. Field studies of chewable tablets containing praziquantel and pyrantel along with other drugs have shown effectiveness against hookworms and roundworms in naturally infected dogs [3]. Other chewable products combine fluralaner, moxidectin, and pyrantel and have shown activity against hookworms and Toxascaris leonina in laboratory studies [4]. Some of these products also target less common parasites such as Angiostrongylus vasorum [5]. The point for owners is simple: many products share ingredients, and your veterinarian is the one who can keep them from stacking.
If your dog takes heart medication, check with your veterinarian before any new dewormer. What Are the Side Effects of Vetmedin for Dogs? explains why drug timing and monitoring matter for dogs with heart disease.
Overdose and When to Call a Veterinarian or Poison Control
An overdose can happen when a dog eats a whole pack of tablets, when two people in the house each give a dose, or when a dog gets a product meant for a larger dog.
Signs of overdose look like the serious side effects listed above, only stronger. Watch for heavy drooling, repeated vomiting, unsteadiness, tremors, or seizures. These can start within hours of the dose.
If you suspect an overdose, call your veterinarian or an animal poison control hotline immediately. Have the product packaging, your dog's weight, and the time of the dose ready. Do not wait for symptoms to appear before you call.
Do not try to make your dog vomit unless a veterinarian tells you to. Some products can cause more harm coming back up.
Limitations and When to Contact a Veterinarian
This article covers the reactions owners see most often, but it cannot tell you what is happening with your individual dog. Every case needs a veterinarian who can examine your dog and review the full medication history.
Use these timing guides:
Call now, same day
- Vomiting that will not stop or happens more than a few times
- Drooling that continues for hours
- Your dog will not eat or drink
- Diarrhea with blood
- Any behavior that seems off to you
Go to an emergency hospital now
- Seizure
- Tremors, twitching, or muscle stiffness
- Wobbliness or trouble standing
- Swelling of the face, hives, or trouble breathing
- Collapse or unresponsiveness
Schedule a routine visit
- Mild sleepiness that lasts into the next day
- Soft stool that clears up on its own
- A question about whether the worms were actually cleared
- Planning the next deworming dose
A follow up fecal test is often the best way to confirm the treatment worked. Worms can be missed on a single sample, and some dogs need a second round.
Frequently Asked Questions
How long do Drontal side effects last in dogs?
Most mild reactions settle within 24 hours. Vomiting and drooling tend to stop within a few hours, while sleepiness and soft stool may linger into the next day. If anything lasts longer than a day or gets worse, call your veterinarian.
Can Drontal make a dog act drunk or wobbly?
Yes, and this is the reaction that worries veterinarians most. Wobbliness, tremors, and twitching are uncommon but serious, and they can appear within hours of the dose. A wobbly dog needs to be seen right away, not monitored at home.
Should I feed my dog before or after giving Drontal?
Many veterinarians suggest a small meal around the time of the dose to reduce stomach upset. Follow the instructions your veterinarian gives you, since the guidance can differ based on your dog's health and the reason for treatment.
What should I do if my dog vomits the tablet right after taking it?
Call your veterinarian before giving another dose. You cannot tell how much of the tablet your dog absorbed, and repeating the full dose could cause an overdose. Your veterinarian may recommend waiting, rechecking a fecal sample, or treating again later.
Is it normal to see worms in my dog's poop after treatment?
Yes, this is expected. The medicine paralyzes or damages the worms, and they pass out in the stool over the next day or two. Seeing worms does not mean the treatment failed. If your dog still has worms weeks later, a follow up fecal test can confirm whether another dose is needed.
Related Articles
- Dog Anxiety Medication Side Effects: What to Watch For
- What Are the Side Effects of Bravecto for Dogs? What to Watch For
- What Are the Side Effects of Vetmedin for Dogs?
- What Are the Side Effects of Antibiotics in Dogs?
- What Are the Side Effects of Clavamox for Dogs?
- What Are the Side Effects of Trazodone for Dogs?
- Drontal for Dogs: Dosage, Frequency, and Safety
- Drontal for Dogs: How to Give It and What to Expect
- Drontal for Cats: Side Effects and What to Expect
References
- Field efficacy of Febantel, Pyrantel embonate and Praziquantel (Drontal® Tasty) against naturally acquired intestinal helminths of hunting dogs in southern Italy. Parasites & vectors, 2025.
- Ocular Manifestations in Dogs With Facial Nerve Dysfunction. Veterinary ophthalmology, 2026.
- Field efficacy and safety evaluation of a novel chewable tablet (Credelio Quattro™) containing lotilaner, moxidectin, praziquantel, and pyrantel against gastrointestinal nematode infections in dogs in the USA. Parasites & vectors, 2025.
- Efficacy evaluation of a new oral chewable tablet containing fluralaner, moxidectin, and pyrantel (BRAVECTO® TriUNO) against hookworm and Toxascaris leonina infections in a non-terminal study design in dogs. Parasites & vectors, 2026.
- Efficacy of a single oral administration of a formulation of fluralaner, moxidectin and pyrantel (BRAVECTO® TriUNO) in dogs for the treatment and prevention of angiostrongylosis. Parasites & vectors, 2026.