Hydrocodone for Dogs: Dosage Chart by Weight, Side Effects

Hydrocodone is a prescription opioid we use in dogs to quiet a dry, hacking cough that won't settle on its own. In dogs it's a cough suppressant rather than a pain medication, and it isn't the first thing I reach for. I use it when the coughing itself has become the problem.

What is hydrocodone, and how does it work?

Hydrocodone is a semi-synthetic opioid made from codeine. In dogs we use it for one job: turning down a cough.

It works on the cough centre in the brainstem rather than on the throat or the airway itself. Hydrocodone is a mu-opioid receptor agonist, so it binds the same receptors as morphine and codeine, and acting there it raises the threshold your dog's body needs to reach before it triggers a cough.² It may also cut back the amount of mucus the airway lining produces, though the mechanism for that isn't well understood.²

Two things surprise owners about it.

The first is that it's a poor pain medication in dogs. It's an opioid, so people assume it doubles as pain relief. In practice it isn't reliable for that, and I almost never prescribe it for pain. If pain is what we're treating, tramadol or an anti-inflammatory is a better conversation.

The second is that no hydrocodone product is approved for animals. Every prescription I write for a dog is extra-label use of a human medication, which is normal and legal in veterinary practice, but it does mean the label on the bottle is written for people and won't mention dogs anywhere.

What does hydrocodone treat in dogs?

Hydrocodone treats a persistent dry cough that's wearing your dog out. It's the first-choice opioid cough suppressant in dogs because its effect is measurable and fairly reliable, which isn't true of every option on the list.²

The cases where I consider it look like this:

1. Tracheal collapse. The windpipe softens and flattens, and you get that dry goose-honk cough that feeds on itself. Coughing irritates the airway, which triggers more coughing.
2. Chronic bronchitis. Long-standing airway inflammation with a stubborn cough that has outlived the inflammation causing it.
3. Severe kennel cough. Not routine cases, which resolve on their own. I mean the dog who has been hacking for a week and can't sleep. If you're in the thick of it, our guides on how long kennel cough stays contagious and why vaccinated dogs still catch it are worth reading.
4. Coughing linked to heart disease. An enlarged heart can press on the airway above it. This one comes with a limit: once there's fluid on the lungs, hydrocodone is the wrong answer.

A cough is a protective reflex, and beneficial coughing shouldn't be suppressed.² Finding and treating the cause always comes first. Antitussives earn their place once the underlying problem has been addressed and the cough is still there, or when the cause can't be pinned down and the coughing is doing real harm.^2,4 By that point the coughing is costing your dog sleep, and that alone is reason to treat it.

When hydrocodone is the wrong choice

The cough has to be the right kind, with an established diagnosis. That gets settled with an exam rather than at home, and it's the reason I won't start hydrocodone for a dog I haven't examined.

• Not for a wet or productive cough. If your dog is bringing something up, that cough is clearing the airway. Suppressing it leaves mucus and debris sitting where the infection is.^4,5
• Not with pneumonia. Cough suppressants are usually contraindicated in bacterial pneumonia for the same reason.^4,5
• Not for a dog in heart failure with fluid on the lungs. Heart disease can cause coughing, but once there's pulmonary edema the answer is furosemide and cardiac treatment, not a cough suppressant.
• Not if your dog is coughing up blood. That needs a diagnosis first. Our guide to the common causes of coughing up blood covers what we look for.
• Careful in dogs who already breathe badly. Severe airway disease, flat-faced breeds, and any dog with poor respiratory reserve all sit closer to trouble if an opioid slows their breathing.¹
• A good fit for a chronic, dry, exhausting cough. This is the dog whose underlying disease is already being treated and who is still coughing enough to lose sleep over it.^2,4

Which hydrocodone product will you get in Canada?

Almost certainly a plain hydrocodone bitartrate syrup at 1 mg/mL, sold here as pdp-HYDROCODONE.¹ It's a red, cherry-flavoured liquid, and most dogs take it without much argument.

Most of what you'll find online about hydrocodone in dogs is American, and the American product is different. There it's usually formulated with homatropine, an anticholinergic added to make the taste unpleasant and cut the potential for human misuse.² You'll see it under names like Hycodan, Tussigon and Hydromet. Hycodan is no longer marketed in Canada, so if an article mentions a second ingredient and your bottle only lists one, that's why.

Two practical notes on the Canadian syrup. It's sweetened with sorbitol and sucrose and contains no xylitol, which is the ingredient owners rightly worry about in flavoured liquids.¹ And because it's 1 mg per mL, the millilitres on the syringe match the milligrams in the dose, which makes small-dog dosing much easier to get right than splitting tablets.

What is the dose of hydrocodone for dogs?

The published starting dose is 0.25 mg/kg by mouth, every 6 to 12 hours, moved up or down by about 25% and adjusted to effect.² Older references put the range slightly lower and the interval slightly shorter, at roughly 0.22 mg/kg every 4 to 8 hours.³ Both land in the same place in practice.

Every figure in the table below is a single dose, given every 6 to 12 hours. I start most dogs at the low end and work up. The goal is a dog who coughs little enough to sleep, without being sedated or constipated getting there.²

Use this table to understand the prescription you've been given, not to set one yourself. Your dog's dose depends on their kidney and liver function, their other medications, and what we're actually treating, and the interval matters as much as the number.

If you miss a dose, give it when you remember unless the next one is close, then carry on as normal. Don't double up. If your dog gets more than they should, or gets into the bottle, call us rather than waiting to see what happens. Activated charcoal can help early on, and naloxone reverses opioid effects if it comes to that.¹

What are the side effects of hydrocodone in dogs?

Most dogs tolerate hydrocodone well. The side effects that do show up come from the same opioid receptors that stop the cough, so they scale with the dose.

The two you're most likely to see:

• Sedation. Sleepier than usual, especially in the first few days. It often eases as your dog adjusts. If it doesn't, that's a sign we're at too high a dose rather than a reason to stop.²
• Constipation. Opioids slow the gut down. Oddly, the very first dose sometimes does the opposite and prompts an immediate bowel movement. Watch for straining or two days without a stool, and let us know, because a stool softener or a diet change usually sorts it out.

The ones you're less likely to see:

• Slowed or laboured breathing. Rare at cough-suppressing doses, but it's the reason we're careful with dogs who already have poor lung function.¹
• Trouble urinating. Opioids can affect bladder emptying. A dog who is straining to urinate or going far less than usual needs to be seen.
• Vomiting or an upset stomach. Usually mild and short-lived. Call us if your dog vomits repeatedly.
• Body temperature swings. Running hot or cold turns up mostly with overdoses or in dogs who are unwell for other reasons.

On longer courses, tolerance and physical dependence can develop with repeated dosing, which is true of opioids generally.¹ Practically, that means we don't stop a long course abruptly, and if the medication seems to be losing its effect, the answer is a recheck rather than more of it.

What medications interact with hydrocodone?

Several, which is why we ask what else your dog is on, including supplements and anything prescribed elsewhere.

The interactions sort into three groups.

Drugs that slow hydrocodone's breakdown. Hydrocodone is processed by liver enzymes called CYP3A4 and CYP2D6. Medications that block those enzymes leave more hydrocodone in circulation for longer, so a normal dose starts behaving like a large one. Macrolide antibiotics such as erythromycin and azole antifungals such as ketoconazole are the two that come up most.¹

Drugs that add to the sedation. Anything else that depresses the central nervous system stacks with hydrocodone. That includes other opioids, trazodone, gabapentin, acepromazine and benzodiazepines. We do sometimes pair these on purpose, because sedation can be part of settling a cough. The problem is adding one at home without telling us.

Drugs that affect serotonin. Combining hydrocodone with an SSRI or SNRI raises the risk of serotonin syndrome.¹ This is a different mechanism from the two above. Fluoxetine and amitriptyline don't act on opioid receptors. They matter here because of serotonin and because they also affect the enzymes that clear hydrocodone. Monoamine oxidase inhibitors, the group that includes selegiline, are the strictest of these and shouldn't be combined with hydrocodone at all.¹

This isn't the full list, and some medications belong in more than one group. Bring us the labels and let us sort it out.

What else can we use to control a cough?

Plenty, though treating the underlying disease beats every drug in this table.^2,4 Weight loss for a collapsing trachea, a harness instead of a collar, controlling airway inflammation, treating the heart. Those change the trajectory. Cough suppressants only change the symptom.

When we do need to suppress the cough, these are the realistic options.

There's also work underway on non-opioid cough drugs, including a class called P2X3 receptor antagonists, though dosing in dogs hasn't been established yet.² Nothing there changes what I'd prescribe today, but it's the direction this is heading.

Storing hydrocodone safely at home

Hydrocodone is a Schedule I narcotic under Canada's Controlled Drugs and Substances Act.⁶ That changes a few practical things at home.

We can't authorise a refill over the phone the way we can with most medications, so plan ahead rather than calling on the last day. Keep the syrup in its original bottle, closed, at room temperature and out of sight.¹ Accidental swallowing by a child can be a fatal overdose, and this one tastes like cherry syrup.¹ Don't keep leftovers for next time, and bring unused medication back to us or to a pharmacy for disposal instead of putting it in the bin.

Never give your dog a hydrocodone product from your own medicine cabinet. Many human hydrocodone tablets are combined with acetaminophen, which is toxic to dogs and dangerous to cats.² The prescription we write is a single-ingredient syrup for a reason.

If your dog is coughing and you're not sure whether it's the dry kind we can safely suppress, that's the question to bring us. It's answered with a stethoscope and usually a chest x-ray, and getting it right decides whether a cough suppressant helps your dog or holds them back.