Yes, wormwood is toxic to dogs. The plant contains a chemical called thujone that overstimulates the nervous system and can cause seizures, vomiting, kidney failure, and liver damage. Dogs encounter wormwood most often when owners give it as a “natural” dewormer, but even small amounts of wormwood oil can be dangerous.
Why Wormwood Is Dangerous for Dogs
Wormwood (Artemisia absinthium) is the herb historically used to make absinthe and vermouth. The oil extracted from the plant contains thujone, a compound that directly interferes with how nerve signals work in the brain. Normally, a neurotransmitter called GABA acts as the brain’s braking system, calming nerve activity by opening tiny channels that let chloride ions flow into cells. Thujone blocks this braking system by binding to the same receptor site, effectively removing the brain’s ability to quiet itself down.
Research published in the Proceedings of the National Academy of Sciences confirmed that thujone is a competitive blocker at this receptor. The effect is dose-dependent: the more thujone in the system, the more the brain’s calming signals are suppressed. This is why the primary danger of wormwood poisoning is uncontrolled nervous system excitation, which manifests as tremors, muscle rigidity, and seizures.
Symptoms of Wormwood Poisoning
The neurological symptoms tend to appear first because thujone acts rapidly on the brain. You may notice:
- Tremors or muscle twitching that progress to full seizures
- Restlessness or agitation, since the brain’s calming pathways are blocked
- Vomiting and drooling, often among the earliest signs
- Disorientation or unsteady walking
Beyond the immediate neurological effects, wormwood can damage organs over the following hours and days. The Merck Veterinary Manual notes that elevations in liver enzymes and kidney markers have been reported in cases of wormwood toxicosis. Kidney failure is one of the most serious potential outcomes, particularly with wormwood oil, which contains a concentrated dose of thujone compared to dried leaves or teas.
The “Natural Dewormer” Problem
The name “wormwood” itself suggests antiparasitic properties, and the herb has a long folk history as a dewormer. This leads some dog owners to seek out wormwood tinctures or dried herb products as alternatives to conventional parasite medications. The problem is twofold: there is no established safe dose of thujone for dogs, and the concentration of thujone varies wildly between wormwood products.
Even in human medicine, WebMD notes there isn’t enough reliable information to determine an appropriate dose. For dogs, which are generally more sensitive to plant toxins than humans due to differences in liver metabolism, the margin between a dose that might affect parasites and a dose that causes seizures or organ damage is unknown. Wormwood oil poses the greatest risk because it concentrates thujone far beyond what you’d find in the raw plant. A dog that chews on wormwood growing in a garden faces less danger than one given drops of essential oil, though neither scenario is safe.
What Happens at the Vet
If your dog has ingested wormwood in any form, the priority is stopping the toxin from being absorbed further and managing any seizures that develop. Depending on how recently the ingestion happened, a veterinarian may induce vomiting or use activated charcoal to bind remaining plant material in the stomach.
For dogs already showing symptoms, treatment focuses on intravenous fluids to support kidney function and help flush thujone from the body. The Merck Veterinary Manual recommends monitoring liver and kidney values for several days after exposure, since organ damage can develop on a delayed timeline even after neurological symptoms resolve. If liver values climb, protective medications are started to limit further damage. Dogs that receive prompt treatment before seizures become prolonged or kidney function deteriorates generally have a good chance of recovery.
Which Wormwood Products Are Most Dangerous
Not all wormwood exposures carry the same level of risk. Concentrated wormwood essential oil is by far the most dangerous form because it delivers a large dose of thujone in a small volume. Tinctures and liquid extracts fall in the middle, with variable thujone content depending on the manufacturer. Dried wormwood leaves or tea contain lower concentrations, but can still cause toxicity if a dog eats enough.
Some commercial herbal “deworming” blends for pets include small amounts of wormwood alongside other herbs. These products exist in a largely unregulated space, and the actual thujone content is rarely tested or listed. The absence of a known safe threshold for dogs means any thujone-containing product carries inherent risk, regardless of how it’s marketed. Conventional dewormers prescribed by a veterinarian have established safety profiles and proven effectiveness, which wormwood-based alternatives lack.