A cat with feline hyperesthesia.

Feline Hyperesthesia (FHS)

Ever since the earliest days of human-cat interactions, cats have had a reputation for being mystical, spiritual beings, either divine or possessed. It isn’t hard to understand why. Cats have the propensity to gaze unblinking in people’s eyes, to appear to see things that aren’t there, to run crazily around for no apparent reason, and to go from quiet to ferocious in a moment.

Some of these attributes, in an extreme form, are components of the syndrome known as feline hyperesthesia. Cats affected by this syndrome show the most bizarre character changes, sometimes appearing to hallucinate, act manic, schizophrenic, or even “possessed.”

Clinical Signs of Feline Hyperesthesia Syndrome (FHS)

Possible Causes

FHS tends to arise for the first time in mature cats. No one really knows what causes FHS, but there are a few possibilities:


There is no definitive “rule in” test that confirms FHS. If the clinical picture fits the description above, the diagnosis is confirmed by exclusion of possible medical causes and by a positive response to treatment for FHS. To this end, your veterinarian should obtain a careful behavioral history regarding your cat, perform a thorough physical examination, and take a blood sample for complete blood count, chemistry profile, and thyroid hormone level (T4). Medical conditions that may be confused with FHS include hyperthyroidism (thyroid gland overactivity), brain infections, brain trauma, brain tumors, some poisonings (e.g. lead, strychnine), heavy parasitic infestations of the skin, nutritional deficits (e.g. thiamine), and severe allergy.


Optimize the affected cat’s environment to minimize stress (stress could be – probably is – a factor in every expression of the syndrome). Recommendations include:

Anti-Obsessional/Antidepressant Therapy

Drugs that help are potent serotonin-enhancing medications. In the brain, the neuromodulator, serotonin, stabilizes mood and has anti-obsessional and anti-aggressive effects. Drugs that have been found effective include clomipramine (Clomicalm®) and fluoxetine (Prozac®) though, theoretically, any potent serotonin-enhancing drug, including paroxetine (Paxil®), sertraline (Zoloft®), and fluvoxamine (Luvox®) should all work. These drugs take a while to become effective. Typically nothing much is seen for the first three weeks. Then, by four weeks, owners might notice a 50% reduction in the incidence and severity of bouts of FHS. Typically, the improvement may reach 75% at eight weeks, 85% at 12 weeks, and 95% by sixteen weeks. Complete cure is rare and most cats need to remain on medication long term to suppress the FHS behavior. This need not be a problem since the doses employed are small, therefore inexpensive, and medical complications of treatment are rare. Nevertheless, it makes sense to have treated cats checked by the veterinarian, including appropriate bloodwork, at least once per year.

Anti-Convulsant Therapy

When anti-obsessional therapy is ineffective or only marginally effective, anti-convulsants can be tried. The drug of first choice is usually phenobarbital. Phenobarbital takes three weeks to peak, after which a “trough” blood sample (one taken when the level is expected to be lowest) should be taken to measure the phenobarbital level in plasma. If the level is appropriate for control of seizures, and yet no improvement has occurred, alternative measures will have to be employed. It is possible to combine phenobarbital treatment with anti-obsessional therapy, if necessary.


With appropriate environmental and pharmacologic treatment, affected cats can often be rehabilitated and can lead a normal life. On treatment, most appear much happier than they were previously while suffering the full brunt of their affliction.