Yes, cats have a full endocrine system that produces dozens of hormones governing everything from metabolism and stress responses to reproduction and bone health. These chemical messengers work the same way they do in humans: glands release them into the bloodstream, and they travel to organs and tissues to regulate body processes. Understanding your cat’s hormones helps explain behaviors like spraying, mood changes, and weight fluctuations, and it sheds light on common diseases that show up as cats age.
Thyroid Hormones and Metabolism
The thyroid gland, a two-lobed structure in the neck, produces the hormones T3 and T4 using iodine from the diet. These hormones set the speed of nearly every metabolic process in a cat’s body. In normal amounts, they work alongside growth hormone and insulin to build and maintain tissues. When levels are too low, body processes become sluggish. When levels are too high, those same processes run too fast, breaking down proteins and tissue instead of building them.
Hyperthyroidism, a condition where the thyroid overproduces T3 and T4, is one of the most common hormonal disorders in older cats. Over 10% of cats older than 10 will develop it, with some studies in the UK finding rates near 12% in cats over nine. Signs include weight loss despite a ravenous appetite, restlessness, increased thirst, and a rapid heart rate. The opposite condition, hypothyroidism, is rare in cats but causes lethargy, weight gain, and a dull coat.
Insulin and Blood Sugar
The pancreas produces insulin, the hormone responsible for moving glucose out of the bloodstream and into cells for energy. Cats are especially prone to Type 2 diabetes, which involves a combination of insufficient insulin production and insulin resistance, meaning the body’s cells stop responding normally to the insulin that is produced. When resistance develops, the pancreas has to pump out more and more insulin to achieve the same blood sugar control.
Obesity, old age, physical inactivity, and calorie-dense diets are all recognized risk factors. Indoor cats eating highly digestible, carbohydrate-rich food face a lifetime of elevated insulin demand, which can eventually exhaust the insulin-producing cells in the pancreas. Once blood sugar stays persistently high, a cycle called glucose toxicity kicks in, further suppressing the pancreas’s ability to make insulin. Elevated fatty acids in the blood can trigger a parallel process called lipotoxicity. Burmese cats carry a higher genetic risk than most other breeds.
Cortisol and the Stress Response
When a cat perceives a threat, the brain signals the adrenal glands to release cortisol through a chain called the hypothalamic-pituitary-adrenal axis. This is the same stress hormone humans produce, and it serves the same purpose: mobilizing energy, raising alertness, and suppressing inflammation in the short term. In cats, even routine stressors like car rides, vet visits, and blood draws measurably raise cortisol levels. One study found that each additional needle stick during a veterinary procedure increased cortisol by a small but significant amount, and the longer a cat spent out of its carrier, the higher cortisol climbed.
Chronic stress is where cortisol becomes a problem. Cats living in unpredictable environments, multi-cat households with conflict, or homes with frequent disruption can maintain elevated cortisol for extended periods. This suppresses immune function, can worsen skin conditions, and contributes to behavioral issues like inappropriate elimination and overgrooming. Interestingly, calming medications that visibly relax a cat at the vet don’t necessarily lower cortisol. Research has shown that cats given a common pre-appointment sedative appeared calmer to their owners and veterinarians, but their cortisol levels remained just as high, suggesting the internal stress response continued even when outward signs faded.
Reproductive Hormones
Unspayed female cats cycle through dramatic hormonal shifts during their heat cycles. Estrogen rises sharply during estrus (the “in heat” phase), staying high for three or four days before dropping abruptly. These elevated estrogen levels drive the calling, rolling, and restless behavior owners recognize during heat. Unlike dogs, cats are induced ovulators, meaning they typically don’t release eggs until mating occurs. If ovulation happens, progesterone takes over, rising within 24 hours and peaking around 15 to 25 days later. During pregnancy, progesterone stays elevated until just before birth. Between heat cycles, both hormones drop to baseline, and the behavioral signs disappear.
In male cats, testosterone drives territorial marking, roaming, mating vocalizations, and certain types of aggression. After neutering, testosterone doesn’t vanish overnight. Levels begin declining over the first two to four weeks, and owners typically notice subtle early shifts like reduced restlessness and fewer escape attempts. More obvious changes, like a significant drop in spraying and fighting, usually emerge between one and three months post-surgery. Cats neutered later in life may take longer, and some behaviors that became habitual before surgery can persist even after testosterone is gone.
Oxytocin and Social Bonding
Cats produce oxytocin, the same hormone associated with bonding and trust in humans. Recent research measuring salivary oxytocin in pet cats found that the hormone’s response to owner interaction depends on the cat’s attachment style. Cats classified as securely attached, those that initiate contact, hover near their owner, and show few escape attempts, experienced a significant rise in oxytocin during interaction. Cats with anxious attachment styles actually showed a trend toward decreasing oxytocin during the same interactions, and their baseline oxytocin levels were higher to begin with.
Securely attached cats also initiated more interactions with their owners and had fewer owner-reported behavioral problems. Their owners, in turn, engaged in less forced interaction (picking the cat up when it didn’t approach, for example). The findings suggest that the hormonal reward system in cats mirrors what’s seen in dogs and humans: positive, voluntary social contact triggers oxytocin release, reinforcing the bond.
Calcium-Regulating Hormones
Tiny parathyroid glands, located near or embedded within the thyroid, produce parathyroid hormone (PTH), which is the primary regulator of calcium in a cat’s blood. When calcium drops, PTH signals the kidneys to hold onto calcium and excrete phosphorus, stimulates bone to release stored calcium, and promotes the formation of active vitamin D, which in turn boosts calcium absorption from food. Working in the opposite direction, the thyroid also produces calcitonin, which lowers blood calcium by slowing the cells that break down bone. Together, these two hormones keep calcium and phosphorus within a narrow range that’s critical for nerve function, muscle contraction, and heart rhythm.
Growth Hormone
Cats produce growth hormone in the pituitary gland at the base of the brain. In kittens, it drives normal development. In adult cats, it continues to play a role in tissue maintenance. Rarely, a pituitary tumor causes the gland to overproduce growth hormone, a condition called acromegaly. Affected cats develop broadened facial features, enlarged paws, organ enlargement (particularly the liver and kidneys), and weight gain despite having diabetes that’s unusually difficult to control with insulin. About half of acromegalic cats develop noisy breathing from thickened tissue in the throat. Because there’s no single diagnostic test, veterinarians rely on a combination of physical signs, blood markers, and brain imaging to confirm it.
How Hormonal Problems Show Up
Many feline hormonal disorders share overlapping symptoms, which can make them tricky to spot early. Increased thirst and urination show up in hyperthyroidism, diabetes, and acromegaly. Weight changes go in different directions depending on the condition: hyperthyroid cats lose weight while eating more, diabetic cats may lose or gain weight, and acromegalic cats tend to gain. Behavioral shifts like increased aggression, anxiety, or lethargy can all trace back to hormonal imbalances rather than personality changes.
Because many of these conditions cluster in middle-aged and senior cats, routine bloodwork after age seven or eight gives your vet a baseline to catch hormonal shifts before they cause serious damage. Thyroid levels, blood sugar, and kidney values are all part of standard senior panels, and early detection typically means simpler, more effective treatment.