Hops: Dog Poisoning, Allergy and Beer

Table of Contents

1. Hops and Dogs: The Finding in Brief
2. The First Report: Five Dogs, Four Deaths
3. 71 Cases From Two Centres
4. 177 Calls to a Poison Helpline
5. Who the Findings Matter Most For
6. Allergy in People
7. Sedation and Medicines
8. Breastfeeding
9. Beer Is Not a Hops Supplement
10. Children, Pregnancy and Other Groups
11. What Remains Unknown
12. Key Research Papers
13. Connections

Hops and Dogs: The Finding in Brief

Three veterinary case series in the citation set describe the same pattern:

• Dogs develop hyperthermia (a dangerously high body temperature), rapid breathing, a racing heart, restlessness and vomiting within hours of eating hops.
• Most dogs that reach treatment survive, but some die despite intensive care.
• The higher the temperature, the greater the risk of death.

The amounts involved are small by kitchen standards: in one series, the median amount eaten was 2 ounces (about 57 g) in survivors and 2.5 ounces (about 71 g) in dogs that died (Pfaff and colleagues, 2022). Veterinary emergency literature continues to discuss the problem, including a 2022 letter on hops toxicosis in dogs (Bates and colleagues, 2022).

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The First Report: Five Dogs, Four Deaths

The case that put hops on the veterinary map was published in 1997 (Duncan and colleagues, 1997). Five dogs, four of them Greyhounds, ate spent hops, the wet cone residue discarded after brewing.

• Clinical signs began an average of 3 hours after eating.
• Signs included marked hyperthermia, restlessness, panting, vomiting, signs of abdominal pain and seizures.
• Four of the five dogs died despite aggressive treatment, and three showed a rapid onset of rigor mortis.

The authors noted that Greyhounds were over-represented and that the signs resembled malignant hyperthermia, an inherited condition in which muscles generate runaway heat in response to a trigger. They also raised the possibility that hops contain a substance that uncouples oxidative phosphorylation, the process cells use to turn fuel into usable energy; when it is uncoupled, the energy is released as heat instead. Neither explanation has been proven, and the specific toxic compound is not identified in these reports.

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71 Cases From Two Centres

A retrospective study reviewed 71 dogs with known hops ingestion from a national animal poison control centre database and a university veterinary medical record system, covering 2002 to 2014 (Pfaff and colleagues, 2022).

• Hyperthermia occurred in 96% (68 of 71) of dogs.
• The most common signs on arrival were hyperthermia and a fast heart rate; both were significantly higher in dogs that died.
• 59 dogs (77%) survived with intensive treatment. All survivors recovered completely by discharge.
• The median time to death among non-survivors was 10.7 hours (range 2 to 30 hours).
• After adjustment for cooling, time to presentation and drug treatment, every degree of temperature rise was associated with a 78% higher chance of death.
• Survivors were brought in slightly sooner (5.0 versus 5.5 hours).
• None of the decontamination, cooling or drug measures evaluated (dantrolene, cyproheptadine, sedatives) was associated with better survival in this group.

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177 Calls to a Poison Helpline

A second retrospective study looked at 177 calls about hops ingestion in dogs to a pet poison helpline between 2005 and 2018 (Becker and colleagues, 2023).

• Clinical signs appeared in 74.0% (131 of 177) of dogs; the rest showed none.
• The most common signs were rapid breathing (98 of 131), hyperthermia (65 of 131) and vomiting (44 of 131).
• Most symptomatic dogs developed signs between 2 and 8 hours after eating hops.
• Severe hyperthermia, above 41.4 °C (106 °F), developed in 8 dogs, and 3 of them died. A fourth dog was found dead at home.
• Outcomes were known for 83 dogs; 79 of 83 (95.2%) survived, and in all but one survivor signs resolved within 24 hours.
• Hops calls rose as a share of all the helpline's cases over the 13 years.

The authors concluded that prognosis is generally good but that some dogs develop severe, fatal hyperthermia. The higher survival than in the 71-case series may partly reflect which cases each source captured: a quarter of the helpline dogs never showed signs at all.

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Who the Findings Matter Most For

The case reports point to the settings where dogs meet hops:

• Home brewing. The first report involved spent hops discarded after brewing (Duncan and colleagues, 1997).
• Greyhounds were over-represented in that first report, which is why a malignant-hyperthermia-like susceptibility has been suggested. The larger series found no significant difference between survivors and non-survivors by breed, sex or age (Pfaff and colleagues, 2022).

The studies agree that speed matters: shorter time to presentation was associated with survival in the 71-case series. Questions about a pet that may have eaten hops are a matter for a veterinarian or an animal poison helpline.

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Allergy in People

LactMed, the U.S. National Library of Medicine's database on drugs and supplements in breastfeeding, states that allergy to hops occurs rarely. The citation set for this page does not contain clinical studies of hop allergy or of occupational allergy in hop pickers or brewery workers; the records returned by the allergy search were off-topic and were not used. Beyond the statement that it is rare, the frequency and forms of hop allergy are therefore not described here.

The EMA, in its assessment of hop strobile as a herbal medicine, reported that no side effects had been reported with these medicines at the time of its review. EMA: Lupuli flos

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Sedation and Medicines

• Sedation. LactMed states that hops can cause sedation and advises against use alongside other sedating drugs and in people with depression.
• Liver drug-clearing enzymes. In human liver preparations in the laboratory, valerian and valerian–hops extracts reduced glucuronidation of paracetamol (acetaminophen), oestradiol, morphine and testosterone, and reduced the activity of two key enzymes (UGT1A1 and UGT2B7) (Alkharfy and Frye, 2007). Whether this changes drug levels in people has not been tested.
• Trials. In the largest valerian–hops trial, there were no serious adverse events, no significant carry-over effects the next day, and no rebound insomnia after stopping (Morin and colleagues, 2005).
• Hormone-like activity. Hop extracts contain 8-prenylnaringenin, described as the most potent phytoestrogen known (Stevens and Page, 2004); see 8-Prenylnaringenin and Menopause for the hormone-related questions.

Questions about combining hops with prescribed medicines are for a pharmacist or clinician.

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Breastfeeding

Hops are sometimes promoted for increasing breast-milk supply. LactMed reports that:

• hops is a purported galactogogue (a milk-increasing substance);
• some animal evidence indicates a hop polysaccharide can raise prolactin, the milk-producing hormone, but a small study in humans found that a hop soup appeared to lower serum prolactin;
• no data exist on the excretion of hop components into breast milk or on safety and efficacy in nursing mothers or infants;
• some sources advise against hops during breastfeeding because of its phytoestrogen content.

LactMed also notes that dietary supplements may differ from their labels and that testing on one product may not apply to another.

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Beer Is Not a Hops Supplement

Beer is the main way people encounter hop compounds (Stevens and Page, 2004), and a review of beer and skin health lists the polyphenols, bitter acids and prenylflavonoids that hops add to it (Chen and colleagues, 2014). The same review states that epidemiological evidence linking beer to skin conditions is limited, that direct clinical evidence for beer compounds is lacking, and that their bioavailability and any health effects at moderate beer consumption still need to be determined.

There are three reasons beer cannot stand in for a hop preparation in the research:

1. Alcohol. Beer contains ethanol, which has well-documented effects of its own. See Alcohol and Alcohol Use Disorder.
2. Amounts. How much of beer's hop compounds the body absorbs has not been determined (Chen and colleagues, 2014), and the 8-PN derived from the precursor xanthohumol was undetectable in most people even after a 180 mg single dose of xanthohumol (Legette and colleagues, 2014).
3. The sleep study used no alcohol. The only sleep study of beer in this citation set used non-alcoholic beer (0.0%): 17 shift-working nurses fell asleep faster on actigraphy (12.01 versus 20.50 minutes) with 333 ml at supper for 14 days, in an unblinded comparison with their own control period (Franco and colleagues, 2012).

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Children, Pregnancy and Other Groups

• Children. The EMA monograph limits hop strobile medicines to adults and adolescents over 12.
• Pregnancy. No pregnancy studies appear in the citation set for this page, so there is no good safety data to report.
• Depression. LactMed lists depression as a reason it advises against hops, because of its sedative effect.
• Women's health botanicals in general have not been rigorously tested for toxic effects or drug interactions, according to a 2016 pharmacology review (Dietz and colleagues, 2016).

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What Remains Unknown

1. Which hop compound causes hyperthermia in dogs, and why some dogs are affected and others are not.
2. How common hop allergy is, and in whom.
3. Whether the laboratory effects on liver enzymes change drug levels in people.
4. Safety in pregnancy and breastfeeding.
5. Long-term safety of 8-PN-standardised extracts.

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Key Research Papers

1. Duncan KL, Hare WR, Buck WB. Malignant hyperthermia-like reaction secondary to ingestion of hops in five dogs. Journal of the American Veterinary Medical Association. 1997;210(1):51-4. PubMed PMID: 8977648
2. Pfaff A, Sobczak BR, Babyak JM, et al. Retrospective analysis of hops toxicosis in dogs (2002-2014): 71 cases. Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001). 2022;32(1):90-97. PubMed PMID: 34498796
3. Becker J, Brutlag AG, Hovda L, et al. A retrospective evaluation of hops ingestion in 177 dogs (2005-2018). Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001). 2023;33(3):348-353. PubMed PMID: 36908194
4. Bates N, Tizzard Z, Edwards N. Hops toxicosis in dogs. Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001). 2022;32(2):274. PubMed PMID: 34850534
5. Hops. Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Institute of Child Health and Human Development; 2006–. PubMed PMID: 30000893
6. Alkharfy KM, Frye RF. Effect of valerian, valerian/hops extracts, and valerenic acid on glucuronidation in vitro. Xenobiotica; the fate of foreign compounds in biological systems. 2007;37(2):113-23. PubMed PMID: 17484515
7. Morin CM, Koetter U, Bastien C, et al. Valerian-hops combination and diphenhydramine for treating insomnia: a randomized placebo-controlled clinical trial. Sleep. 2005;28(11):1465-71. PubMed PMID: 16335333
8. Stevens JF, Page JE. Xanthohumol and related prenylflavonoids from hops and beer: to your good health! Phytochemistry. 2004;65(10):1317-30. PubMed PMID: 15231405
9. Chen W, Becker T, Qian F, et al. Beer and beer compounds: physiological effects on skin health. Journal of the European Academy of Dermatology and Venereology : JEADV. 2014;28(2):142-50. PubMed PMID: 23802910
10. Legette L, Karnpracha C, Reed RL, et al. Human pharmacokinetics of xanthohumol, an antihyperglycemic flavonoid from hops. Molecular nutrition & food research. 2014;58(2):248-55. PubMed PMID: 24038952
11. Franco L, Sánchez C, Bravo R, et al. The sedative effect of non-alcoholic beer in healthy female nurses. PloS one. 2012;7(7):e37290. PubMed PMID: 22815680
12. Dietz BM, Hajirahimkhan A, Dunlap TL, et al. Botanicals and Their Bioactive Phytochemicals for Women's Health. Pharmacological reviews. 2016;68(4):1026-1073. PubMed PMID: 27677719

PubMed Topic Searches

1. PubMed: Hops toxicosis in dogs
2. PubMed: Hops and malignant hyperthermia in dogs
3. PubMed: Hops (Humulus lupulus) allergy

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Connections

• Hops (Humulus lupulus) — the main page for the plant
• Hops Benefits Deep Dive — the evidence ledger
• Sleep and the Valerian Combination — the sleep trials
• 8-Prenylnaringenin and Menopause — the hormone questions
• Xanthohumol Research — the most-studied hop compound
• Alcohol — the toxin in beer
• Alcohol Use Disorder — when drinking becomes a disorder
• Fever (Pyrexia) — how fever differs from hyperthermia
• Rhabdomyolysis — muscle breakdown, a complication of extreme overheating
• Valerian — hops' usual partner in sleep products
• Kava — another calming herb, with safety questions of its own

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