CBD for Dogs with Seizures: What Colorado State's Study Found

If your dog has epilepsy and the medications aren't fully controlling the seizures, you're living in a very specific kind of fear. You count the days between episodes. You watch for the warning signs. And you've probably already searched for anything that might reduce the frequency, even slightly.

CBD oil for dogs with seizures is one of the most researched applications of cannabidiol in veterinary medicine. Unlike some CBD uses where the evidence is thin, the seizure data comes from a randomized, placebo-controlled clinical trial at Colorado State University, the same level of evidence that human pharmaceuticals require.

Here's what that study found, what it means for your dog, and what your veterinarian needs to know.

The Colorado State University Seizure Trial

McGrath et al. (2019) published the landmark study in the Journal of the American Veterinary Medical Association (JAVMA). This is the study that changed the conversation about CBD and canine epilepsy.

Study Design

• 26 dogs with intractable idiopathic epilepsy (seizures not fully controlled by existing medication)
• Randomized, placebo-controlled, double-blind, the gold standard for clinical evidence
• All dogs continued their existing anti-seizure medications (phenobarbital, potassium bromide, or both)
• Treatment group received 2.5 mg/kg CBD twice daily for 12 weeks
• CBD was administered as a purified CBD oil in MCT coconut oil carrier

Results

Additional findings:

• No dogs achieved complete seizure freedom (0 seizures) during the trial
• The response was variable: some dogs had dramatic reductions, others had modest improvement
• Higher baseline CBD plasma levels correlated with greater seizure reduction
• CBD was administered alongside existing medications, not as a replacement

What This Means

CBD appears to work as an adjunctive therapy, a supplement to existing anti-seizure medication that provides additional seizure reduction. It is not a cure. It is not a replacement for phenobarbital or potassium bromide. It's an add-on that reduced seizure frequency in the majority of dogs studied.

For a dog parent watching their pet seize 4 times a month, a 33% reduction means roughly one fewer seizure per month. For some families, that's significant.

The ALP Question: Liver Enzymes and CBD

The McGrath study also reported something that matters if your dog is already on anti-seizure medication: elevated alkaline phosphatase (ALP) levels in the CBD group.

ALP is a liver enzyme. Elevated ALP can indicate liver stress. Here's the context you need:

• Phenobarbital already elevates ALP. It's a known, expected side effect of long-term phenobarbital use. Most epileptic dogs on phenobarbital have elevated ALP at baseline.
• CBD added further ALP elevation in some dogs. The increases were statistically significant but remained within ranges that the study's veterinary team did not consider clinically dangerous.
• No dogs developed liver failure or required treatment withdrawal due to liver enzyme changes during the 12-week trial.
• Other liver enzymes (ALT, GGT) were not significantly affected.

The practical takeaway: if your dog takes phenobarbital and you add CBD, your veterinarian should monitor liver enzymes more frequently, every 4–6 weeks initially, rather than the standard every 6–12 months. This isn't a reason to avoid CBD. It's a reason to add it under veterinary supervision with appropriate monitoring. For more on how CBD interacts with specific prescription drugs, see our CBD vs gabapentin and CBD vs trazodone comparisons.

The Seizure Protocol: How to Use CBD

Dosing

The McGrath protocol is specific: 2.5 mg/kg twice daily. This is higher than the general wellness or anxiety dose, and it's the only seizure protocol supported by a published RCT.

For a weight-specific calculation, use our CBD dosing calculator and select "Seizures / Epilepsy" as the condition.

Critical Rules

1. Do NOT stop existing anti-seizure medication. CBD was tested as an add-on, not a replacement. Abruptly stopping phenobarbital or potassium bromide can trigger status epilepticus, a life-threatening seizure emergency.
2. Inform your veterinarian. Your vet needs to know you're adding CBD, both for the CYP450 drug interaction and for the ALP monitoring protocol.
3. Maintain consistent timing. Every 12 hours, with food. Inconsistent dosing undermines the steady blood levels that the protocol relies on.
4. Track seizure frequency. Keep a seizure diary: date, time, duration, severity, and any identifiable triggers. Without data, you can't evaluate whether CBD is working. A minimum evaluation period is 8–12 weeks of consistent dosing.
5. Start at full dose. Unlike anxiety or wellness protocols where we recommend starting at 50% and ramping up, the McGrath study used 2.5 mg/kg from day one. Discuss with your vet whether ramping is appropriate for your specific dog.

Drug Interactions: The CYP450 Factor

CBD inhibits cytochrome P450 (CYP450) liver enzymes. This is critically relevant for epileptic dogs because their existing medications are metabolized through the same pathway.

Phenobarbital + CBD

CBD can increase phenobarbital blood levels by slowing its hepatic metabolism. This means your dog's existing phenobarbital dose may become more potent when CBD is added. Signs of phenobarbital toxicity include excessive sedation, incoordination, and increased drinking/urination. Your vet may need to reduce the phenobarbital dose.

Potassium Bromide + CBD

Potassium bromide (KBr) is primarily excreted by the kidneys, not metabolized by liver CYP450 enzymes. The CBD interaction with KBr is therefore less concerning than with phenobarbital. However, the combination hasn't been specifically studied, and monitoring remains advisable.

Levetiracetam (Keppra) + CBD

Levetiracetam is increasingly used as a first-line or adjunctive anti-seizure drug in dogs. It has minimal hepatic metabolism, which theoretically makes the CYP450 interaction less relevant. Limited data exists on the specific CBD-levetiracetam combination in dogs.

Zonisamide + CBD

Zonisamide is partially metabolized by CYP3A enzymes in the liver. CBD's CYP450 inhibition could affect zonisamide clearance. If your dog takes zonisamide, blood level monitoring is advisable after adding CBD.

The message is the same regardless of medication: your veterinarian needs to be involved. CBD interactions with anti-seizure drugs aren't theoretical concerns. They're pharmacological realities that require professional management.

What's Happened Since the McGrath Study

The 2019 McGrath trial opened the door. Subsequent research has expanded the picture:

• The AKC Canine Health Foundation has funded additional CBD and epilepsy research, reflecting institutional recognition that the preliminary data warrants follow-up investigation.
• Larger multi-site trials are underway to confirm the McGrath results in bigger populations and explore optimal dosing ranges. The original 26-dog trial was small by pharmaceutical standards.
• Combination cannabinoid studies are exploring whether CBD combined with CBDA (cannabidiolic acid) or other minor cannabinoids produces superior seizure control compared to CBD alone.
• Refractory epilepsy studies continue to show that CBD's benefit is most pronounced in dogs whose seizures aren't adequately controlled by conventional medication alone.

The evidence trajectory is positive but incomplete. More data is coming. For now, the McGrath protocol remains the clinical reference point.

What to Tell Your Veterinarian

Many dog owners are uncomfortable telling their vet about CBD use. Here's what your vet needs to hear:

1. "I want to add CBD as an adjunct to [current medication]." Frame it as an add-on, not a replacement. This matches the published evidence and signals you're not planning to stop their prescribed protocol.
2. "The McGrath 2019 study at Colorado State used 2.5 mg/kg twice daily and showed 89% of dogs had reduced seizure frequency." Give them the citation. Many vets haven't seen the data.
3. "I know CBD can affect liver enzymes and interact with phenobarbital via CYP450." This shows you've done your homework and understand the monitoring requirements.
4. "Can we set up a monitoring schedule for ALP and phenobarbital blood levels?" Proactively asking for monitoring builds trust and ensures safety.

If your vet is unfamiliar with the research, point them to the JAVMA publication (PubMed ID: 31067185) and the AKC Canine Health Foundation summary.

Product Considerations for Seizure Management

Seizure management has stricter product requirements than general wellness or anxiety:

• Consistent potency is critical. Batch-to-batch variation in CBD content means your dog's actual dose varies. Choose products with tight label accuracy (±10% on COA) and buy the same product consistently.
• Higher concentrations needed. At 2.5 mg/kg twice daily, a 60-pound dog needs 68 mg per dose. A 500 mg / 30 mL bottle (16.7 mg/mL) requires 4 mL per dose, so that bottle lasts just 4 days. Look for 1,000+ mg bottles for medium and large dogs.
• THC content must be verified. THC can lower seizure threshold in some animals. Broad-spectrum or isolate products are preferred. If full-spectrum, verify THC below 0.1% on the COA.
• MCT carrier oil preferred. The McGrath study used CBD in MCT coconut oil. Matching the carrier oil matches the study's bioavailability conditions.

For our full product evaluation methodology and verified picks, see our CBD vs hemp oil comparison for understanding what's in different products. For cat-specific dosing (no published feline seizure data exists), see our cat CBD guide. If your epileptic dog also has anxiety triggers (fireworks, storms), see our fireworks anxiety protocol and thunderstorm anxiety guide. The drug interaction considerations in those articles are especially important for dogs already on anti-seizure medication. For dogs dealing with both epilepsy and a cancer diagnosis, our CBD for dogs with cancer guide covers the specific CYP450 interaction risks. For safety thresholds and what to do if you accidentally give too much, see can dogs overdose on CBD.

Epilepsy rarely travels alone, and the same liver-enzyme and CYP450 considerations that shape seizure dosing apply whenever CBD sits alongside other prescriptions — the rest of the research collected here at CBD Oil Pets connects those interaction and monitoring points across conditions so you and your vet can build one coherent plan.

Frequently Asked Questions

Does CBD stop seizures in dogs?

CBD does not stop seizures entirely. The Colorado State trial (McGrath et al. 2019) found that 89% of dogs had fewer seizures when CBD was added to their existing medication, with a median 33% reduction in seizure frequency. No dogs in the study achieved complete seizure freedom. CBD is an adjunctive therapy. It supplements existing anti-seizure medication, not replaces it.

How much CBD should I give my epileptic dog?

The published protocol is 2.5 mg/kg of body weight twice daily (every 12 hours). For a 50-pound dog, that's approximately 56 mg per dose. This dose was used in the Colorado State trial and is the only seizure-specific CBD protocol supported by a randomized controlled trial. Administer with food for better absorption. Use our CBD dosing calculator for your dog's exact weight.

Can I give my dog CBD instead of phenobarbital?

No. CBD was studied as an add-on to existing anti-seizure medication, not as a replacement. Abruptly discontinuing phenobarbital can trigger status epilepticus, a life-threatening seizure emergency. Never change your dog's anti-seizure medication regimen without your veterinarian's direct guidance. CBD is a supplement to the protocol, not the protocol itself.

Will CBD interact with my dog's seizure medication?

Yes. CBD inhibits cytochrome P450 (CYP450) liver enzymes, which can increase blood levels of phenobarbital. This may require your vet to reduce the phenobarbital dose. CBD also caused elevated alkaline phosphatase (ALP) in the Colorado State study. Your veterinarian should monitor liver enzymes every 4 to 6 weeks when starting CBD alongside anti-seizure medication.

How long does CBD take to reduce seizure frequency?

The Colorado State trial assessed outcomes over 12 weeks. Seizure frequency reduction was measured cumulatively over this period. A minimum evaluation period of 8 to 12 weeks of consistent, twice-daily dosing is necessary before determining whether CBD is effective for your individual dog. Keep a seizure diary to track frequency, duration, and severity.