Hops (Humulus lupulus) in Pets

Hops and spent brewing mash trigger fatal malignant hyperthermia and extreme fevers in dogs. Review signs, breed risks, and urgent cooling care.

What It Is

Hops are the female cone-like flowers (strobiles) of the hop vine (Humulus lupulus), widely cultivated and used in brewing for their bittering resins and aromatic essential oils. The active chemical constituents include alpha-acids (humulone, cohumulone, adhumulone), beta-acids (lupulone), and volatile terpene oils. When ingested by domestic canines, unknown compounds in hops act as an uncoupler of oxidative phosphorylation in cellular mitochondria. This uncoupling disrupts cellular energy production and triggers uncontrollable, explosive metabolic heat generation known as malignant hyperthermia.

Where Pets Come Across It

Dogs encounter hops in residential environments primarily through home brewing activities. The most dangerous and palatable source is spent brewing hops—the boiled mash left behind after wort production. Spent hops retain toxic resins while absorbing sweet, aromatic malt sugars, making them exceptionally tempting to scavenging dogs. Less commonly, dogs consume raw dried hop pellets or fresh hop vines growing in home gardens.

Which Animals Are Affected

Only dogs: Merck notes there are no reports of hops poisoning in other species. Pet Poison Helpline says any dog can be affected, but breeds prone to malignant hyperthermia, including Greyhounds, Labrador Retrievers, Saint Bernards, pointers, Dobermans, Border Collies and American Cocker Spaniels, are at higher risk.

Published Toxic Dose

There is no established toxic dose for hops. Merck notes that hops poisoning has been reported only in dogs and that the exact mechanism is unknown. Pet Poison Helpline treats any ingestion of hops, fresh, dried or spent from home brewing, as potentially serious.

Signs and How Soon They Appear

Merck reports that signs develop within 8–24 hours and last 24–48 hours. They include a very high body temperature (malignant hyperthermia), a fast heart rate, rapid breathing, vomiting, diarrhoea and either agitation or lethargy. The temperature can rise quickly, so a dog that has eaten hops needs a vet before signs start.

What to Do Right Now

Call your vet or an emergency clinic straight away, before signs appear. The vet may make the dog vomit and give activated charcoal. Treatment of malignant hyperthermia includes active cooling, which Merck describes as important for success, and the muscle relaxant dantrolene in severe cases. Do not give human fever medicines.

The home brewing hazard: why spent hops are deadly

Home craft brewing has surged in popularity, bringing an acute canine hazard into domestic kitchens and gardens. During beer brewing, hops are boiled in sugary malt wort to extract bitterness and aroma. When the boil finishes, the spent hops are strained out and often discarded into garden compost piles or open kitchen bins. Unlike fresh bitter hops, spent hops are steeped in sweet malt sugars that dogs find irresistible. A dog can eat a large amount from a bin or compost heap in a few minutes. Always dispose of brewing waste inside sealed, dog-proof bins.

Frequently Asked Questions

Sources and References

• Merck Veterinary Manual: Hops Toxicosis (Dietary and Herbal Supplements)
• Pet Poison Helpline: Hops

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