Last updated: April 6, 2026

Trilostane (Vetoryl) for Dogs: Cushing’s Disease Treatment Guide

When a veterinarian diagnoses your dog with Cushing’s disease, the conversation about treatment almost always turns to one medication: trilostane for dogs, sold under the brand name Vetoryl. It is the most widely prescribed drug for managing hyperadrenocorticism — the medical name for Cushing’s disease — and for good reason. When dosed correctly and monitored carefully, trilostane can dramatically improve a dog’s quality of life, easing the excessive thirst, pot-bellied appearance, hair loss, and relentless panting that make the condition so uncomfortable.

But trilostane is not a simple medication to give and forget. It requires precise dosing, regular blood tests, and a genuine partnership between you and your veterinarian. This guide walks you through everything you need to know about trilostane for dogs — from how it works at the cellular level to what daily life with the medication actually looks like.

What Is Trilostane and How Does It Work?

Trilostane is a synthetic steroid analogue that works by inhibiting an enzyme called 3-beta-hydroxysteroid dehydrogenase. This enzyme is essential for the production of cortisol in the adrenal glands. By blocking it, trilostane reduces the amount of cortisol the adrenal glands can manufacture and release into the bloodstream.

It is important to understand that trilostane does not destroy adrenal tissue or cure the underlying cause of Cushing’s disease. In most cases, the root problem is a small tumor on the pituitary gland that keeps telling the adrenal glands to produce cortisol. Trilostane does not address that tumor — it simply reduces the adrenal glands’ ability to follow the instruction. This is why the medication must be given every day for the rest of the dog’s life. If you stop giving trilostane, cortisol production will climb back up and symptoms will return.

Trilostane is effective for both pituitary-dependent Cushing’s disease, which accounts for roughly 80 to 85 percent of cases, and adrenal-dependent Cushing’s disease caused by adrenal tumors. It is the first-line medical treatment recommended by veterinary endocrinologists in most countries, having largely replaced the older drug mitotane (Lysodren) due to its more predictable safety profile.

When Is Trilostane Prescribed?

Not every dog diagnosed with Cushing’s disease needs immediate treatment. Veterinarians generally recommend starting trilostane for dogs when clinical signs are significantly affecting quality of life. The symptoms that most commonly prompt treatment include:

• Excessive thirst and urination that disrupts the household routine or causes house-training accidents
• Recurrent skin or urinary tract infections driven by immune suppression from elevated cortisol
• Significant muscle wasting or weakness that limits the dog’s mobility and enjoyment of daily activities
• Progressive hair loss or skin fragility that causes discomfort or increases infection risk
• Uncontrolled appetite leading to obesity or behavioral problems around food
• Heavy panting at rest that interferes with sleep for both the dog and the owner

If a dog has mild symptoms and is otherwise comfortable, some veterinarians may recommend watchful waiting with regular check-ups rather than jumping straight to medication. The decision is always individualized based on the dog’s age, overall health, severity of symptoms, and the owner’s ability to commit to ongoing monitoring.

Trilostane Dosage for Dogs

Dosing trilostane for dogs is not a one-size-fits-all calculation. Most veterinarians start with a conservative dose and adjust upward based on how the dog responds clinically and what the monitoring blood tests show.

Starting dose. The typical initial dose ranges from 1 to 2.5 milligrams per kilogram of body weight, given once daily. Some veterinarians prefer to start at the lower end of this range — closer to 1 mg/kg — to minimize the risk of over-suppression. The capsules come in several sizes (5 mg, 10 mg, 30 mg, 60 mg, and 120 mg), and your veterinarian will choose the combination closest to the target dose for your dog’s weight.

Once-daily versus twice-daily dosing. Trilostane’s effects on cortisol last approximately 8 to 12 hours in most dogs. For this reason, some dogs do well on once-daily dosing, while others need the total daily dose split into two doses given roughly 12 hours apart. If a dog’s symptoms are well controlled in the morning but seem to return by evening — increased thirst, restlessness, or panting — twice-daily dosing may be recommended.

Giving it with food. Trilostane should always be administered with a meal. Food significantly increases the absorption of the drug. Giving it on an empty stomach can result in erratic absorption and unpredictable cortisol levels. A consistent feeding and dosing schedule helps keep cortisol suppression steady throughout the day.

Dose adjustments. Based on monitoring test results and clinical response, the dose may be increased, decreased, or the dosing schedule may be changed from once to twice daily. These adjustments are a normal and expected part of trilostane therapy. It can take several weeks to months to find the ideal dose for an individual dog.

Monitoring and ACTH Stimulation Tests

One of the most important aspects of trilostane for dogs is the monitoring protocol. Unlike many medications where you simply give a pill and watch for improvement, trilostane requires regular blood testing to ensure cortisol is being suppressed to a safe and effective level — not too much and not too little.

The ACTH stimulation test is the primary monitoring tool. It involves taking a blood sample to measure baseline cortisol, injecting synthetic ACTH (which stimulates the adrenal glands to produce cortisol), and then taking a second blood sample one to two hours later. The post-ACTH cortisol level tells the veterinarian how much reserve capacity the adrenal glands have while the dog is on trilostane.

The target post-ACTH cortisol level is generally between 1.45 and 9.1 micrograms per deciliter (40 to 250 nmol/L), though many veterinarians aim for the middle of that range. Values below 1.45 suggest over-suppression and the dose should be reduced. Values above 9.1 suggest the dose may need to be increased if symptoms persist.

Typical monitoring schedule:

• 10 to 14 days after starting trilostane or after any dose change
• 4 weeks after starting treatment
• 12 weeks (3 months) after starting treatment
• Every 3 to 6 months thereafter for the life of the dog

Timing matters. The ACTH stimulation test should be performed 4 to 6 hours after the morning dose of trilostane is given with food. Testing at the wrong time can give misleading results. If your veterinary appointment is at an odd time, discuss with your vet whether to adjust when you give the morning dose on test day.

In addition to the ACTH stimulation test, veterinarians typically check a complete blood count, chemistry panel, and electrolytes at each monitoring visit. These tests help detect early signs of complications such as electrolyte imbalances, kidney changes, or liver enzyme elevations.

Side Effects and Risks of Trilostane

Like all medications that affect hormone production, trilostane carries real risks. Most dogs tolerate it well, but owners need to know what to watch for and when to act.

Common side effects that are usually mild and may resolve as the body adjusts include:

• Decreased appetite or mild nausea, particularly in the first few days
• Lethargy or reduced energy
• Mild vomiting or soft stools
• Temporary increase in thirst during the adjustment period

Serious side effects that require immediate veterinary attention include:

• Addisonian crisis (hypoadrenocorticism). This is the most dangerous potential complication. If trilostane suppresses cortisol too aggressively, the dog can develop a life-threatening cortisol deficiency. Signs include severe lethargy, weakness, collapse, vomiting, diarrhea, loss of appetite, and shaking. An Addisonian crisis is a veterinary emergency — if you notice these signs, stop the trilostane and get to a veterinary clinic immediately.
• Adrenal necrosis. In rare cases, trilostane can cause permanent destruction of adrenal gland tissue. This is uncommon but has been documented and can result in the dog requiring lifelong cortisol supplementation, essentially developing permanent Addison’s disease.
• Electrolyte imbalances. Changes in sodium and potassium levels can occur, particularly if adrenal suppression is excessive. This is one reason regular blood work is essential.

The key to minimizing risk is consistent monitoring. Dogs that receive trilostane for dogs with regular ACTH stimulation tests and dose adjustments have a far better safety record than those whose monitoring lapses.

What Improvement Looks Like

When trilostane is working at the right dose, the changes can be remarkably encouraging. Most owners notice the first improvements within the first two to four weeks of treatment.

Thirst and urination are usually the first symptoms to improve. Many owners report that their dog’s water intake drops noticeably within the first week or two. The desperate, constant drinking slows, and house-training accidents become less frequent or stop entirely.

Energy and muscle tone improve over the first one to three months. Dogs that had become lethargic and weak often regain interest in walks, play, and daily activities. Muscle mass gradually rebuilds as cortisol levels normalize.

Coat and skin are the slowest to respond. Hair regrowth can take three to six months or longer. The skin gradually thickens and becomes less fragile. Recurrent infections become less frequent as the immune system recovers from chronic cortisol suppression.

Appetite typically normalizes, with the ravenous, desperate hunger giving way to a more normal interest in food. The pot-bellied appearance gradually reduces as abdominal fat redistributes and muscle tone improves.

It is worth noting that trilostane manages Cushing’s disease — it does not cure the underlying tumor. Some symptoms may never completely resolve, and the medication may need periodic dose adjustments as the disease progresses. However, for most dogs, the improvement in quality of life is substantial and meaningful.

Drug Interactions and Precautions

Before starting trilostane for dogs, make sure your veterinarian knows about every medication and supplement your dog takes. Several drug interactions deserve attention.

ACE inhibitors such as enalapril or benazepril, often used for heart disease or protein-losing kidney conditions, can potentially increase the risk of hyperkalemia (elevated potassium) when used alongside trilostane. This combination is not necessarily contraindicated, but electrolytes should be monitored more closely.

Potassium-sparing diuretics such as spironolactone can compound the risk of elevated potassium levels and should be used with caution.

NSAIDs and corticosteroids. Dogs on trilostane should generally avoid non-steroidal anti-inflammatory drugs when possible, as the combination may increase the risk of gastrointestinal ulceration. If your dog requires anti-inflammatory treatment for arthritis or pain, discuss alternatives with your veterinarian. Corticosteroid use would obviously counteract the purpose of trilostane.

Handling precautions. Trilostane capsules should not be opened or crushed, and pregnant women should avoid handling the medication entirely. Trilostane can affect human steroid hormone production, so always wash your hands after handling the capsules.

Cost of Trilostane Treatment

The financial commitment of trilostane therapy is an important practical consideration. The medication itself typically costs between 50 and 200 dollars per month depending on the dog’s size and required dose. Larger dogs need higher doses and therefore more expensive monthly supplies.

Monitoring costs add significantly to the total. Each ACTH stimulation test plus blood work panel can range from 150 to 350 dollars depending on your clinic and location. With the recommended monitoring schedule, the first year of treatment may involve four to six monitoring visits. After the first year, most dogs need testing every three to six months.

While the costs are real, many owners find that the improvement in their dog’s comfort and quality of life makes the investment worthwhile. If cost is a concern, discuss it openly with your veterinarian — there may be options such as compounded trilostane formulations that can reduce the monthly medication expense.

Trilostane Versus Mitotane: How They Compare

Before trilostane became widely available, mitotane (Lysodren) was the standard treatment for Cushing’s disease in dogs. Both drugs remain in use, but they work very differently.

Trilostane inhibits cortisol production — it blocks the enzyme pathway without destroying tissue. Its effects are reversible. If you stop the medication, cortisol production resumes. This reversibility is one of its major safety advantages.

Mitotane destroys the cortisol-producing layers of the adrenal glands. Its effects are more permanent, which means it can be more difficult to control and carries a higher risk of causing an irreversible Addisonian state. The induction phase of mitotane requires particularly close monitoring.

Trilostane is generally considered to have a wider margin of safety and more predictable pharmacology, which is why it has become the first-line choice for most veterinarians. Mitotane may still be recommended in cases where trilostane is not effective, not tolerated, or when the specific clinical situation favors a more aggressive approach. Your veterinarian can help you understand which option is best for your individual dog.

Frequently Asked Questions

How long does it take for trilostane to start working in dogs?

Most owners notice some improvement in thirst and urination within the first one to two weeks. Energy levels and appetite typically improve within the first month. Coat regrowth and skin changes take the longest, often three to six months or more. The full benefit of treatment may not be apparent for several months, and the dose may need adjustment during that time.

What happens if I miss a dose of trilostane?

If you miss a single dose, give the next dose at the regular time — do not double up. Because trilostane’s cortisol-suppressing effects last roughly 8 to 12 hours, a missed dose will allow cortisol to rise temporarily, but one missed dose is unlikely to cause significant harm. If doses are missed regularly, symptoms will return. Set a daily alarm or build the dosing into an existing routine to stay consistent.

Can trilostane cause Addison’s disease in dogs?

Yes, this is the most significant risk. If trilostane suppresses cortisol production too aggressively, the dog can develop signs of hypoadrenocorticism (Addison’s disease). In most cases this is reversible — stopping the medication allows the adrenal glands to recover. In rare instances, permanent adrenal damage (necrosis) can occur, requiring lifelong cortisol supplementation. This is why regular monitoring with ACTH stimulation tests is non-negotiable.

Is trilostane safe for dogs with other health conditions?

Dogs with kidney disease, liver disease, or heart conditions may still be candidates for trilostane, but they require closer monitoring and potentially lower starting doses. Dogs that are pregnant or lactating should not receive trilostane. Your veterinarian will evaluate your dog’s full health picture before starting treatment and adjust the monitoring schedule accordingly.

How long can a dog live on trilostane?

Many dogs live two to four years or more after starting trilostane treatment, and some live significantly longer. Survival depends on multiple factors including the type of Cushing’s disease, the dog’s age at diagnosis, presence of other health conditions, and how well the medication is monitored and adjusted. With consistent treatment and monitoring, most dogs enjoy a good quality of life for a meaningful period after diagnosis.

Should I adopt a dog that is already on trilostane?

Absolutely. Dogs on trilostane for Cushing’s disease can be wonderful companions. They need daily medication and regular veterinary monitoring, but many live active, comfortable lives. These dogs are often overlooked in shelters and rescues because of their medical needs, but adopting a dog with a managed condition can be deeply rewarding. Ask the shelter or rescue for the dog’s medical records, current dosing, and most recent ACTH stimulation test results so your veterinarian can continue treatment seamlessly.

Where can I learn more about breeds prone to Cushing’s disease?

Certain breeds — including Poodles, Dachshunds, Boston Terriers, Boxers, Beagles, and Yorkshire Terriers — develop Cushing’s disease more frequently than others. You can explore breed-specific health information in our dog breeds directory to learn about the conditions your dog’s breed may be predisposed to and what proactive screening looks like.