CBD Side Effects in Dogs: What the Studies Report

CBD is generally well-tolerated in dogs at therapeutic doses. Multiple clinical trials confirm this. But "well-tolerated" does not mean "side-effect-free," and every owner giving their dog CBD should know what to watch for.

This guide covers every documented side effect of CBD in dogs: what the clinical studies actually report, how common each one is, how serious it is, and what to do about it. We also cover the critical distinction between CBD side effects and signs of a contaminated product, because they look different and require different responses.

Side Effects at a Glance

All of these side effects are dose-dependent, meaning they become more likely and more pronounced at higher doses. This is why starting low and increasing gradually is the single most effective way to minimize problems. See our CBD dosage guide for the standard titration protocol.

Drowsiness and Sedation

Sedation is the most frequently reported side effect across all published CBD studies in dogs. It is dose-dependent and generally self-limiting.

Vaughn et al. (2024) documented sedation across multiple dose groups in a 28-day safety study, with higher incidence at 10–20 mg/kg compared to lower doses. Hunt et al. (2023) also reported drowsiness as a primary owner-observed side effect. Verrico et al. (2020) confirmed the dose-dependent nature: sedation increased predictably with dose escalation.

For most dogs, drowsiness is most noticeable in the first 3–5 days and diminishes as the body adjusts. If sedation persists beyond a week, the dose is likely too high.

Gastrointestinal Effects

GI upset (primarily diarrhea, soft stool, and decreased appetite) is the second most commonly reported category of side effects. Vomiting occurs less frequently but is documented.

McGrath et al. (2019) reported GI effects in the epilepsy trial at 2.5 mg/kg twice daily. Vaughn et al. (2024) found GI side effects increased significantly at doses above 10 mg/kg. Flint et al. (2024) added further safety data confirming GI disturbance as a dose-related effect.

Two mechanisms are likely at play. First, CBD itself may affect gut motility through interaction with cannabinoid receptors in the gastrointestinal tract. Second, the carrier oil (typically MCT or hemp seed oil) can cause GI upset independent of the CBD, particularly in dogs with sensitive stomachs or when given on an empty stomach.

Practical Management

• Give CBD with food. This reduces GI irritation from the carrier oil and slows absorption, producing a smoother effect curve.
• Start at the lowest recommended dose and increase over 7–14 days. See our dosing guide for the standard "start low, go slow" protocol.
• Try a different delivery format. Some dogs tolerate CBD treats better than oils because treats deliver CBD with food by default.
• If diarrhea persists beyond 48 hours at a stable dose, discontinue CBD and consult your veterinarian.

ALP (Alkaline Phosphatase) Elevation

This is the side effect that gets the most attention in the veterinary literature, and the one that requires the most nuance to explain.

Gamble et al. (2018) first documented statistically significant ALP elevation in dogs receiving CBD at 2 mg/kg twice daily for osteoarthritis. McGrath et al. (2019) confirmed the finding in epileptic dogs at 2.5 mg/kg twice daily over 12 weeks. Vaughn et al. (2024) observed ALP elevation across dose groups, with the effect more pronounced at higher doses.

What ALP Elevation Means

ALP is a liver enzyme. When it rises, it can signal liver stress, or it can mean nothing clinically significant. ALP rises naturally in growing puppies, in dogs on certain medications (especially corticosteroids), and sometimes for reasons that remain unexplained.

In the CBD studies, ALP elevation was statistically significant but not clinically severe. No dogs in Gamble 2018 or McGrath 2019 developed liver failure or clinical signs of liver disease. Vaughn 2024 noted the elevation did not produce clinical illness during the 28-day study period.

However, this does not mean you should ignore it. ALP elevation becomes concerning when:

• Values exceed 2–3 times the upper reference range
• Other liver enzymes (ALT, GGT) are also elevated
• The dog shows clinical signs (jaundice, lethargy, vomiting, weight loss)
• The dog is already on medications metabolized by the liver

Dry Mouth and Increased Thirst

CBD may reduce saliva production by interacting with cannabinoid receptors in salivary glands. In dogs, this manifests as increased water consumption and, in some cases, drooling followed by marked thirst.

This side effect is primarily documented through owner observation and veterinary anecdotal reports rather than formal study measurement. It is considered mild and manageable.

What to do: Ensure your dog always has access to fresh water. This is especially important if you give CBD before car rides, vet visits, or other situations where water access might be limited.

Lowered Blood Pressure

Higher doses of CBD may cause a temporary drop in blood pressure. In dogs, this can appear as momentary lightheadedness when standing up quickly, or simply as increased lethargy.

At standard therapeutic doses (1–5 mg/kg), clinically significant blood pressure drops are rare. This becomes more relevant at doses above 10 mg/kg or in dogs with pre-existing cardiovascular conditions.

What to do: If your dog seems unusually unsteady after starting CBD (beyond the mild sedation described above), reduce the dose. If the dog has a known heart condition, discuss CBD with your veterinarian before starting.

Drug Interactions: The CYP450 Pathway

This is not a side effect of CBD in isolation. It is a side effect of CBD in combination with other medications, and it is arguably the most important section of this article.

CBD is metabolized by the cytochrome P450 (CYP450) enzyme system in the liver. This is the same enzyme system that processes a large number of veterinary medications. When CBD occupies these enzymes, it can slow the metabolism of other drugs, effectively increasing their concentration in the blood.

Medications with documented or plausible CBD interactions include:

• Phenobarbital: commonly prescribed for seizure disorders. CBD may increase phenobarbital levels, requiring dose adjustment and closer monitoring.
• Gabapentin: used for pain and anxiety. See our CBD vs. gabapentin comparison for the full interaction profile.
• NSAIDs (carprofen, meloxicam): both CBD and NSAIDs stress the liver. Concurrent use increases the importance of liver enzyme monitoring.
• Trazodone: used for situational anxiety. See our CBD vs. trazodone comparison for details on combining these.
• Other CYP450-metabolized drugs: including some antibiotics, antifungals, and cardiac medications.

Side Effects vs. Signs of a Bad Product

This distinction is critical and most CBD side effect articles fail to make it clearly.

Normal CBD side effects (drowsiness, mild GI upset, increased thirst) are dose-dependent, appear at predictable times after administration, and resolve when the dose is reduced or CBD is discontinued.

Signs of a contaminated or mislabeled product look different:

Leafreport's 2020 analysis found that 56% of CBD pet products had inaccurate label claims. Some products contained significantly more or less CBD than stated, and some that claimed to be THC-free contained measurable THC. Dogs are far more sensitive to THC than humans; even small amounts can produce symptoms that look like a severe overdose. See our CBD overdose guide for the full THC toxicity symptom profile.

When to Call Your Veterinarian

Not every side effect requires a vet call. Here is a severity-based framework:

Monitor at Home

• Mild drowsiness that resolves within 8–12 hours
• One episode of soft stool
• Slightly decreased appetite for one meal
• Increased water intake

Call Your Vet (Non-Emergency)

• Drowsiness that persists beyond 24 hours after dosing
• Diarrhea lasting more than 48 hours
• Vomiting more than once
• Appetite loss lasting more than one day
• Any side effect that does not resolve with dose reduction
• ALP elevation found on bloodwork (your vet will advise on next steps)

Emergency Vet / ASPCA Poison Control (888-426-4435)

• Inability to stand or walk
• Tremors or seizure activity
• Severe disorientation or unresponsiveness
• Urinary incontinence
• Any severe symptom after a new product or a product without COA verification

How to Minimize Side Effects

1. Start low, go slow. Begin at 0.5–1 mg/kg and increase by 0.5 mg/kg every 5–7 days. Use our dosing calculator to find the right starting point for your dog's weight.
2. Give CBD with food. Reduces GI irritation and improves absorption consistency.
3. Verify the COA. Ensure the product matches its label, contains no detectable THC (or below 0.3%), and is free of heavy metals, pesticides, and residual solvents.
4. Get baseline bloodwork. A pre-CBD liver panel gives your vet a reference point for monitoring ALP and other enzymes.
5. Tell your vet. Even if your vet is neutral or skeptical about CBD, they need to know your dog is taking it, especially if your dog is on other medications.
6. Watch for the first 7 days. Most side effects appear in the first week. If your dog tolerates the starting dose well, gradual increases are less likely to cause problems.
7. Use the right product for your dog's size. A high-concentration oil designed for large dogs makes it too easy to overdose a small dog. Match the product to the weight range.

Frequently Asked Questions

What are the most common side effects of CBD in dogs?

Drowsiness and GI upset (diarrhea, decreased appetite) are the most frequently reported side effects in clinical studies. Vaughn et al. (2024) and McGrath et al. (2019) both documented these as the primary adverse effects. ALP (liver enzyme) elevation is also consistently reported in bloodwork, though it did not cause clinical illness in any published trial. All side effects are dose-dependent: they increase with higher doses and decrease when the dose is reduced.

Can CBD damage my dog's liver?

Multiple studies have documented ALP elevation in dogs receiving CBD, which indicates the liver is processing the compound. However, no published study has reported liver failure or clinical liver disease from CBD alone. The appropriate response is monitoring, not avoidance: baseline bloodwork before starting CBD, a recheck at 30 days, and every 90 days thereafter. Dogs already on liver-metabolized medications (phenobarbital, NSAIDs) need closer monitoring.

Is it safe to give CBD with other medications?

CBD is metabolized by the CYP450 enzyme system, which also processes many veterinary medications. This means CBD can alter the effective levels of other drugs your dog is taking. Phenobarbital, gabapentin, NSAIDs, and trazodone all have documented or plausible interactions. Never add CBD to an existing medication regimen without consulting your veterinarian first. See our gabapentin comparison and trazodone comparison for specific interaction details.

How do I know if my dog is having a bad reaction to CBD vs. a bad product?

Normal CBD side effects are mild, dose-dependent, and resolve when the dose is reduced. Severe or atypical reactions (inability to stand, tremors, rapid-onset disorientation, severe vomiting) more likely indicate THC contamination or product mislabeling. 56% of CBD pet products are mislabeled (Leafreport 2020). Always verify the product has a current, batch-matched COA from a third-party lab.

Do CBD side effects go away over time?

Most side effects, particularly drowsiness and mild GI upset, diminish within the first 3–7 days as the dog's body adjusts. ALP elevation may persist as long as CBD is being given, which is why ongoing monitoring is recommended. If any side effect worsens rather than improves, reduce the dose or discontinue and consult your vet.