# Selegiline for Dogs: Uses, Doses, and Side Effects Selegiline is a prescription monoamine oxidase type B (MAO-B) inhibitor that veterinarians use most often to treat canine cognitive dysfunction syndrome (CCDS), the age-related decline in memory, awareness, and social behavior that some senior dogs develop. In the United States and several other regions it is specifically labeled for that purpose, and it is marketed for dogs under the brand name Anipryl. Selegiline is also sometimes used as an adjunct in dogs with pituitary-dependent hyperadrenocorticism (Cushing's disease), though that use is not the same as its behavioral label and not every dog with Cushing's is a candidate. This article covers how selegiline works, the labeled and commonly cited dose ranges by indication, the interaction warnings that matter most, a monitoring checklist for cognitive dysfunction, and the side effects owners should watch for. **This article is educational and is not a substitute for veterinary diagnosis or treatment.** ## At a Glance | Item | Detail | |--|--| | Active ingredient | Selegiline hydrochloride (also known as L-deprenyl) | | Drug class | Irreversible monoamine oxidase type B (MAO-B) inhibitor | | Species | Dogs (also used in cats by some clinicians) | | Primary labeled use | Canine cognitive dysfunction syndrome (CCDS) in senior dogs | | Secondary use | Adjunct to mitotane in pituitary-dependent Cushing's disease (not a labeled behavioral use) | | How it is given | By mouth, usually once daily in the morning | | Onset | Clinical response is typically assessed after 30 to 60 days of treatment [1] | | Duration of effect | Enzyme inhibition is long-lasting because the drug binds MAO-B irreversibly, so missed doses do not reverse effects quickly | | Prescription status | Prescription only in the United States | | Human antidepressant status | Selegiline is not approved for treating human depression in the context discussed here, and its veterinary use should not be confused with human psychiatric dosing | ## What Selegiline Is and What It Is Labeled For Selegiline, also called L-deprenyl, is a selective inhibitor of monoamine oxidase type B. Monoamine oxidase is an enzyme that breaks down monoamine neurotransmitters, including dopamine. By blocking MAO-B, selegiline slows the breakdown of dopamine in the brain, which is the mechanism that underlies both its use in canine cognitive dysfunction and its historical role as an adjunct in Parkinson's disease in people [2]. In dogs, the primary labeled indication is canine cognitive dysfunction syndrome. CCDS is a diagnosis of exclusion, meaning other painful conditions and health problems that can look similar must be ruled out before the diagnosis is confirmed [3]. Signs include house-soiling, changes in sleep-wake cycles, disorientation, reduced interaction with family members, and declines in activity. Selegiline is the pharmaceutical most often recommended by veterinarians for managing CCDS in the United States, and it is also the medication most often regarded as the most effective option, though only about 30 percent of surveyed veterinarians held that view [4]. That statistic reflects real uncertainty in the field about how well any single treatment works. Selegiline is not approved for treating human depression in this context, and the doses used in canine cognitive dysfunction are distinct from human psychiatric dosing. Owners should not assume that effects or doses transfer between species. ## How Selegiline Works in the Dog Selegiline binds irreversibly to MAO-B. Once bound, the enzyme cannot recover function, and the body must synthesize new enzyme to restore MAO-B activity. This is why the drug's effect persists beyond the drug's own presence in the blood. The pharmacokinetics of selegiline in dogs are unusual. In a study of four female dogs given selegiline intravenously and orally at 1 mg/kg, the mean terminal half-life was about 60 minutes, with rapid oral absorption peaking at roughly 25 minutes. Absolute oral bioavailability was low, averaging 8.5 percent [2]. Low bioavailability means a relatively small fraction of an oral dose reaches systemic circulation unchanged, which is one reason the drug is well tolerated at typical clinical doses. Metabolism matters. Selegiline is metabolized into L-methamphetamine and N-desmethylselegiline, among other products [5]. In dogs given oral L-deprenyl at 0.1, 0.5, and 1.0 mg/kg daily for three weeks, plasma amphetamine levels rose in a dose-dependent way and were undetectable five days after the last dose. MAO-B in brain, liver, and kidney was inhibited in a dose-dependent manner, while MAO-A was not significantly inhibited [6]. That selectivity for MAO-B over MAO-A is important. It helps explain why selegiline at labeled doses does not usually cause the hypertensive "cheese effect" that nonselective MAO inhibitors can, at least until the dose rises high enough to lose selectivity. ## Dose Table by Indication Dose information below is drawn from studies and prescribing references that state explicit numbers. Any dose must be confirmed by the prescribing veterinarian against the current product label. | Indication | Species | Route | Dose as stated in source | Source | |--|--|--|--|--| | Canine cognitive dysfunction syndrome | Dog | Oral | 0.5 to 1.0 mg/kg once daily for 60 days in a 641-dog open-label study | [1] | | Canine cognitive dysfunction, labeled product range | Dog | Oral | Follow the current Anipryl label as directed by the prescribing veterinarian | [7] | | Pituitary-dependent Cushing's disease, adjunct to mitotane | Dog | Oral | Follow the current Anipryl label (the Cushing's indication uses a specific product label, not the CCDS general range) | [7] | | Experimental pharmacokinetic study | Dog | Oral or IV | 1 mg/kg single dose | [2] | Two important cautions on this table. First, the 0.5 to 1.0 mg/kg range comes from a single open-label clinical study, not a randomized controlled trial, and it should be treated as the range that study reported rather than a fixed prescription. Second, the Cushing's use of selegiline is a distinct indication with its own label directions, and it is not interchangeable with the CCDS dose. Owners should never adjust from one indication to another on their own. A separate toxicology study in dogs found that transdermal selegiline systems delivering up to 8.5 mg/kg/day caused no degenerative or life-threatening effects, but did produce increases in alanine aminotransferase at higher exposures [8]. That study used a transdermal system, not the oral product, so it does not define a safe oral ceiling. It does show that the drug has a wide margin before severe toxicity appears in dogs, at least in that experimental setting. ## Giving Selegiline to Your Dog Selegiline is given by mouth, usually once daily in the morning. Morning dosing reduces the chance of interference with sleep, since the drug can be activating in some dogs. Give it with or without food unless the label or your veterinarian says otherwise. Practical points. 1. Give the dose at about the same time each day. Consistency helps you and your veterinarian judge whether the drug is working. 2. Do not double up if you miss a dose. Skip the missed dose and resume the normal schedule. Ask your veterinarian how to handle missed doses for your dog specifically. 3. Do not stop selegiline suddenly without discussing it with your veterinarian, especially if the dog has been on it for weeks or months. 4. Keep the medication away from other pets and children, and store it according to the label. 5. If your dog is on any other medication, including over-the-counter products, supplements, or flea and tick preventives, tell your veterinarian before starting selegiline. ## MAOI Interaction Warnings: The Most Important Safety Section Selegiline is a monoamine oxidase inhibitor. That single fact drives most of the serious interaction risk. Combining an MAOI with drugs that increase serotonin, norepinephrine, or dopamine can cause serotonin syndrome, hypertensive crisis, or other life-threatening reactions. Never combine selegiline with the following without explicit veterinary direction. - Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, sertraline, paroxetine, and fluvoxamine. - Tricyclic antidepressants (TCAs), such as amitriptyline, clomipramine, and imipramine. - Tramadol, which has serotonergic and noradrenergic activity. - Sympathomimetics, including pseudoephedrine, phenylephrine, and amphetamine-type stimulants. - Other MAO inhibitors, including the antiparasitic drug amitraz found in some tick collars and dip products. Washout periods matter. If a dog is switching from an SSRI or TCA to selegiline, or from selegiline to one of those drugs, there must be a washout interval between the last dose of one and the first dose of the other. The exact washout length depends on the specific drug and its half-life, so your veterinarian must specify it. Do not guess. Serotonin syndrome signs to watch for include agitation, restlessness, tremors, muscle rigidity, dilated pupils, excessive panting, vomiting, diarrhea, elevated body temperature, and in severe cases seizures or collapse. These are emergencies. Call your veterinarian or an animal poison control center immediately if they appear. Because selegiline is metabolized in part to L-methamphetamine, there is also a theoretical concern with drugs or foods that raise blood pressure. At labeled doses the risk is low, but it is not zero, and it increases if the dose is raised. Discuss any new medication, including human prescriptions, with your veterinarian before adding it. ## How Well Selegiline Works for Canine Cognitive Dysfunction The evidence for selegiline in CCDS is real but modest, and the field itself is uncertain. A large open-label study of 641 dogs with clinical signs consistent with CCDS treated with selegiline at 0.5 to 1.0 mg/kg once daily for 60 days found that 77.2 percent of dogs showed overall improvement by day 60. Response rates by clinical sign ranged from 67.8 percent for activity or sleep-wake cycle signs to 77.8 percent for disorientation and interaction with family members. Responses at day 30 and day 60 were similar [1]. Because that study was open-label and noncomparative, improvement could reflect the drug, owner expectation, the natural course of the condition, or a combination. A 2025 survey of 318 United States veterinarians found that selegiline was the pharmaceutical most often recommended for CCDS and was also most often considered the most effective, but only about 30 percent of respondents held that effectiveness view [4]. The same survey found that most veterinarians (about 80 percent) rarely or never referred potential CCDS cases to a specialist, and that lack of knowledge and owner-related barriers such as cost or lack of interest were named as factors limiting treatment [4]. In other words, selegiline is widely used but not universally regarded as a strong performer, and many dogs receive it without specialist input. Selegiline is one of several options for cognitive decline in senior pets. A review of therapeutic options notes that drugs, nutritional supplements, and diets are all used, and that cognitive dysfunction should be diagnosed only after other painful conditions and health problems that can mimic it have been ruled out [3]. Selegiline's role is best understood as one part of a broader plan that includes environmental enrichment, routine, and management of concurrent medical problems, not as a standalone cure. ## Mechanism and Decision Path The diagram below traces the typical decision path from suspected cognitive dysfunction through diagnosis, treatment, and monitoring. ```mermaid flowchart TD A[Owner notices behavior change] --> B[Veterinary visit] B --> C{Other causes ruled out} C -->|No| D[Diagnose and treat other condition] C -->|Yes| E[Diagnosis of cognitive dysfunction] E --> F[Discuss options with veterinarian] F --> G[Start selegiline if appropriate] G --> H[Recheck at 30 days] H --> I{Improvement seen} I -->|Yes| J[Continue and monitor] I -->|No| K[Reassess and adjust plan] ``` ## Side Effects and What to Do Selegiline is generally well tolerated in dogs at labeled doses, but side effects do occur. In the 641-dog open-label study, the most frequently reported adverse events were diarrhea (4.2 percent), anorexia (3.6 percent), and vomiting or salivation (3.4 percent) [1]. These are the side effects owners are most likely to see. Most are mild and often resolve without stopping the drug, but persistent vomiting, refusal to eat, or significant diarrhea needs a veterinary call. Other side effects reported with selegiline in dogs include restlessness, agitation, lethargy, and changes in behavior that can look like the condition being treated. A toxicology study of transdermal selegiline in dogs found increases in alanine aminotransferase in higher-dose groups and pigment in Kupffer cells of the liver at higher exposures, without other consistent adverse clinical chemistry findings [8]. That study used a different route and much higher exposures than typical oral treatment, so it should not be read as a warning about routine oral use, but it does mean liver values are worth monitoring in dogs on long-term therapy. What to do about side effects. 1. Mild, occasional vomiting or soft stool. Note it, keep monitoring, and mention it at the next recheck. 2. Persistent vomiting, diarrhea, or refusal to eat for more than 24 hours. Call your veterinarian. 3. Agitation, tremors, rigidity, dilated pupils, or excessive panting. These could be serotonin syndrome. Treat as an emergency. 4. Any new behavior that concerns you. Call your veterinarian rather than adjusting the dose yourself. ## Which Dogs Should Not Receive Selegiline Selegiline should not be given to dogs with known hypersensitivity to the drug or its components. It should also be used with great caution or avoided in dogs taking any of the interacting drugs listed above, including SSRIs, tricyclics, tramadol, and sympathomimetics. Extra caution applies in these situations. - Dogs with liver disease, since the liver metabolizes selegiline and liver values can change on treatment [8]. - Dogs with pre-existing behavioral conditions such as anxiety or aggression that are already being managed with other psychoactive drugs. - Dogs on amitraz-containing tick control products, because amitraz is itself an MAO inhibitor. - Pregnant or breeding dogs, where safety has not been established for the intended use. - Dogs with uncontrolled seizures, since the drug affects monoamine signaling in the brain. Your veterinarian will weigh these factors for your dog specifically. Do not make the decision on your own. ## Monitoring Checklist for Canine Cognitive Dysfunction Monitoring is as important as the prescription itself. Use this checklist as a starting point and adapt it with your veterinarian. **Behavior scores** 1. Track the specific signs you first noticed, such as house-soiling, nighttime waking, staring at walls, getting stuck in corners, or reduced greeting behavior. 2. Score each sign on a simple 0 to 3 scale (0 = not present, 3 = severe) once a week and bring the numbers to every recheck. 3. Note changes in interaction with family members and in activity level, since these are the domains that showed the clearest response in the largest selegiline study [1]. 4. Keep a sleep-wake log for one week before each recheck. **Appetite** 1. Record whether your dog finishes meals and whether it is eating at normal speed. 2. Weigh your dog monthly or at every visit. Unexplained weight loss is a reason to call. 3. Anorexia was reported in 3.6 percent of dogs in the open-label study [1], so a clear decline in appetite is a known possibility. **Vomiting and gastrointestinal signs** 1. Note how often your dog vomits and whether it is food, bile, or something else. 2. Note stool consistency and frequency. 3. Diarrhea was reported in 4.2 percent of dogs and vomiting or salivation in 3.4 percent in the open-label study [1]. **Serotonin syndrome signs** 1. Watch for agitation, restlessness, tremors, muscle rigidity, and dilated pupils. 2. Watch for excessive panting, drooling, vomiting, and diarrhea that come on suddenly after a new medication is added. 3. Watch for elevated body temperature, seizures, or collapse. These are emergencies. 4. Any cluster of these signs after a new drug is started is a reason to stop the new drug and call your veterinarian immediately. **Liver values** 1. Ask your veterinarian about baseline and periodic blood work, since elevated ALT was seen at higher selegiline exposures in a toxicology study [8]. 2. Report yellowing of the gums or eyes, which can indicate liver problems. **Overall recheck timing** 1. Expect a recheck at about 30 days after starting, since responses at day 30 and day 60 were similar in the largest study [1]. 2. Continue rechecks every one to three months while on treatment, or as your veterinarian recommends. 3. Bring your behavior scores, appetite notes, and any side effect log to each visit. ## How Selegiline Compares With Alternatives Selegiline is one of several products used for cognitive decline in senior dogs. A review of therapeutic options describes drugs, nutritional supplements, and diets as the main categories, and notes that some products have been evaluated in clinical trials while others have only theoretical support [3]. Selegiline is the drug most often recommended by veterinarians in the United States for CCDS [4], which makes it the usual first pharmaceutical choice even though only about 30 percent of surveyed veterinarians considered it the most effective [4]. When selegiline does not produce the hoped-for response, the next steps usually involve reassessing the diagnosis, adding or changing environmental management, addressing concurrent medical problems, and considering other therapies. The 2025 survey found that most veterinarians rarely or never refer CCDS cases to a specialist [4], but referral to a [veterinary behaviorist](/knowledge/veterinary-medicine/anxiety-and-behavior-support/veterinary-behaviorist-when-to-refer) or internist is reasonable for dogs that do not respond or that have complicated concurrent disease. Selegiline is also used as an adjunct to mitotane in dogs with pituitary-dependent Cushing's disease. That use is separate from the CCDS indication and has its own product label directions [7]. It is not a substitute for mitotane and is not appropriate for every Cushing's patient. ## Questions to Ask Your Veterinarian Bring these questions to your first conversation about selegiline. 1. Does my dog's history and examination support a diagnosis of cognitive dysfunction, and what other conditions have been ruled out? 2. Is selegiline the right choice for my dog, and what else should we be doing at the same time? 3. What dose are you prescribing, and how does it map to my dog's weight? 4. What time of day should I give it, and what do I do if I miss a dose? 5. Is my dog on any medication that could interact with selegiline, including flea and tick products? 6. What side effects should I watch for, and which ones mean I should call immediately? 7. When should we recheck, and what will we use to judge whether it is working? 8. What is the plan if we do not see improvement by the first recheck? ## Limitations and When to Contact a Veterinarian Every dog is different, and the dose and plan that suit one dog may not suit another. Response to selegiline is judged over weeks, not days, and the largest study reported improvement at 30 and 60 days [1]. If you do not see change by the first recheck, that is a reason to reassess, not a reason to give up on the diagnosis or the plan. Contact a veterinarian promptly if any of the following occur. - Your dog stops eating for more than 24 hours. - Vomiting or diarrhea persists or is severe. - You see agitation, tremors, rigidity, dilated pupils, or excessive panting, especially after a new medication is added. - Your dog collapses, has a seizure, or seems to be in pain. - Your dog's behavior changes suddenly or worsens after starting treatment. - You are unsure whether a new medication or supplement is safe to give alongside selegiline. For any suspected poisoning or severe reaction, contact your veterinarian, an emergency veterinary hospital, or an animal poison control center right away. ## Frequently Asked Questions ### What is selegiline used for in dogs? Selegiline is a prescription MAO-B inhibitor used mainly to treat canine cognitive dysfunction syndrome, the age-related decline in memory and behavior in senior dogs. It is also sometimes used as an adjunct in pituitary-dependent Cushing's disease. ### Is selegiline the same as Anipryl? Anipryl is a brand name for selegiline hydrochloride marketed for dogs. The active ingredient is selegiline, also called L-deprenyl. ### How long does selegiline take to work in dogs? Response is usually judged after about 30 to 60 days of treatment. In the largest study, responses at day 30 and day 60 were similar, so a reasonable first recheck is around 30 days. ### What are the most common side effects of selegiline in dogs? The most frequently reported side effects are diarrhea, anorexia, and vomiting or salivation. ### Can selegiline be given with fluoxetine or tramadol? No. Selegiline should never be combined with SSRIs like fluoxetine, tricyclic antidepressants, or tramadol without explicit veterinary direction, because of the risk of serotonin syndrome. A washout period is required when switching between these drugs. ### What are the signs of serotonin syndrome in dogs? Signs include agitation, restlessness, tremors, muscle rigidity, dilated pupils, excessive panting, vomiting, diarrhea, elevated body temperature, and in severe cases seizures or collapse. These are emergencies. ### Is selegiline approved for human depression? Selegiline is not approved for human depression in the context of its veterinary use, and human psychiatric dosing should not be applied to dogs. The dose your veterinarian prescribes is specific to your dog. ### Can I stop selegiline suddenly? Do not stop selegiline suddenly without talking to your veterinarian. Sudden discontinuation can cause behavioral changes, and your veterinarian may want to taper or adjust other parts of the plan. ## Related Articles - [Cat Prednisolone for Allergies: Side Effects and Safe Use](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-prednisolone-allergies) - [Dog Prednisone for Allergies: Side Effects and Safe Use](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/dog-prednisone-allergies) - [Prednisone for Dogs: Uses, Side Effects, and Safety Guidelines](/knowledge/veterinary-medicine/preventive-care/prednisone-for-dogs-uses-side-effects-and-safety-guidelines) - [What Are the Side Effects of Gabapentin for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-cats) - [What Are the Side Effects of Clavamox for Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/clavamox-side-effects-dogs) - [What Are the Side Effects of Apoquel for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/apoquel-side-effects-cats) - [Prednisolone Acetate: Uses, Doses and Side Effects](/knowledge/veterinary-medicine/clinical-pharmacology/prednisolone-acetate-uses-doses-and-side-effects) - [Metoclopramide for Dogs: Dose, Uses, Side Effects](/knowledge/veterinary-medicine/pet-medication-guide/metoclopramide-for-dogs-dose-uses-side-effects) - [Proin for Dogs: Uses, Doses, and Side Effects](/knowledge/veterinary-medicine/pet-medication-guide/proin-for-dogs-uses-doses-and-side-effects) ## Sources 1. 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[Toxicokinetic evaluation of a selegiline transdermal system in the dog.](https://pubmed.ncbi.nlm.nih.gov/9099452/)