December 09, 2013
By Dr. Becker
Serotonin is a neurotransmitter produced by the body that plays a role in regulating behavior, awareness of pain, appetite, movement, body temperature, and function of the heart and lungs. Too little serotonin in the brain is thought to play a role in depression. Too much serotonin can lead to excessive nerve cell activity, which in turn can cause a potentially deadly condition known as serotonin syndrome (SS).
The incidence of serotonin syndrome in both pets and people has been on the rise over the last 10 to 15 years due to the increased use of antidepressants, especially selective serotonin reuptake inhibitors (SSRIs) and selective norepinephrine reuptake inhibitors (SNRIs). In the traditional veterinary community, these drugs are prescribed to treat behaviors including depression, anxiety, and obsessive-compulsive disorder.
Medications and Supplements Associated with Serotonin Syndrome in Pets
Medications and supplements that have been implicated in serotonin syndrome in pets include human prescriptions like SSRI and SNRI antidepressants, and monoamine oxidase inhibitors (MAOIs); veterinary prescriptions to alter behavior, including Clomipramine and Fluoxetine; Mirtazapine (an appetite stimulant used primarily in cats); illicit drugs like amphetamines; atypical antipsychotics; certain miscellaneous drugs like opioid painkillers, cough suppressants, migraine medications, anti-viral drugs, and drugs for Parkinson’s Disease; and holistic supplements including serotonin, tryptophan, and St. John’s wort.
Holistic supplements alone are almost never the cause of serotonin syndrome. The problem arises when well-meaning pet owners combine natural supplements and prescribed medications that both act on serotonin levels. S-adenosylmethionine (SAMe) -- a supplement commonly used for mental, liver, and joint support -- should also be avoided in combination with serotonergic agents, as should food high in tyramine (e.g., aged cheese, dried meats/fish, soy). If your pet is taking a drug intended to alter his behavior, you should consult your holistic veterinarian before also giving supplements used for the same purpose.
A special note regarding the supplement tryptophan: The FDA recalled this supplement back in 1989 for political rather than public health reasons. Unfortunately, tryptophan received a bad rap as a result. Tryptophan supplements are as safe and potentially effective as any other supplement, but again, it’s important to talk with your holistic vet about what supplements are best for your pet.
Causes, Symptoms and Diagnosis of Serotonin Syndrome in Pets
In humans, serotonin syndrome is most often seen when two or more drugs that alter serotonin metabolism are taken at the same time. In pets, most SS cases are the result of accidental ingestion or overdose of a single drug (prescribed for either human or veterinary use). Dogs are at higher risk than cats due to their indiscriminate eating habits. It’s not uncommon for dogs to swallow an entire prescription of psychotropic or other drugs at one sitting.
Symptoms of SS in pets can include agitation, depression, aggression, vocalization, seizures, lack of coordination, muscle rigidity, muscle twitching, muscle spasms, tremors, change in heart rate, elevated blood pressure, changes in skin color, hyperthermia, and diarrhea.
No specific test exists to detect serotonin syndrome, so your veterinarian will need to know your pet’s history of drug ingestion, evaluate clinical signs of the condition, and conduct blood tests to check for infection as well as unknown substances your pet may have ingested. Neurological testing to measure reflexes and coordination will also be performed to help pinpoint the specific areas of the nervous system that are affected.
Treatment of Serotonin Syndrome
If drug ingestion or overdose is caught early enough – usually within 30 minutes – activated charcoal may be given to try to limit the amount of drug absorbed into the animal’s system. This is especially important if extended- or sustained-release medications have been ingested. If the pet is stable and the drug is still in the stomach, vomiting may be induced or the stomach may be pumped to remove the drug from the body.
Targeted drugs may be administered to manage severe central nervous system effects, seizures, and severe tachycardia (rapid heartbeat). Drugs known to block the effects of serotonin may be given to help manage symptoms of agitation, hyperthermia and vocalization.
Fluid therapy is also an important feature of managing SS to help support the cardiovascular system and protect the kidneys. And needless to say, all medications and supplements that may increase serotonin levels should be discontinued.
If treated quickly, serotonin syndrome is less likely to be fatal. When the condition results from immediate-release types of medications, symptoms will diminish within 12 to 18 hours. If the product ingested was extended- or sustained-release, the pet can be symptomatic for up to 48 to 72 hours.
How to Treat Your Pet’s Behavior Issues Without Drugs
As a general rule, I don’t believe in using psychotropic drugs as a first line of defense to treat emotional or behavioral issues in animals. They are sometimes appropriate in extreme, intractable cases and/or when a pet is causing harm to himself. Sometimes, they can be used as an interim measure to interrupt the cycle of behavior at the same time other less harmful remedies are being attempted.
But my general recommendation is to try a wide variety of natural remedies first, since every drug has side effects, and there’s always at least some risk of overdose.
- If your pet hasn't been seen by a vet in six months or longer, I recommend scheduling a wellness exam. Illness in animals can cause stress and affect mood, so you’ll want to rule out any underlying physiological issues that may be contributing to behavior or emotional problems.
- Evaluate your pet’s diet and consider transitioning to a fresh, balanced, species-appropriate diet. Switching an animal to the right food can sometimes improve certain behavior problems.
- Dogs and cats get bored just like we do, and boredom can be stressful. Increased daily exercise for dogs and environmental enrichment for kitties can be tremendously beneficial in curbing undesirable behaviors.
- Consult your holistic veterinarian about natural calming remedies like OptiBalance Pet Formulas or Spirit Essences. You can also investigate using herbs and nutraceuticals such as 5-HTP, calming milk protein, l-theanine, ashwagandha, vitamin B3 and B6, GABA, rhodiola, holy basil (Tulsi), and chamomile. There are also excellent traditional Chinese herbs that can reduce anxiety, as well as homeopathic remedies.
Most importantly, I recommend trying to address the root cause of your pet's issues through behavior modification and training for the best long-term success. And if you feel your pet's anxiety is getting worse, consider consulting with a board certified veterinary behaviorist.