How to Tell If Your Cat Is in Pain: Veterinary Guide to Signs and the Feline Grimace Scale

The evolutionary biology of feline pain

To recognize pain in our feline companions, we must understand their wild heritage. The domestic cat (Felis catus) directly descends from the African wildcat (Felis lybica), an obligate solitary hunter.

In nature, a limping, vocalizing, or sluggish cat signals vulnerability to larger predators and rival cats competing for hunting territory. To survive, cats evolved an extraordinary ability to mask overt signs of physical suffering.

Consequently, when an owner finally notices that their cat seems "a bit off," it is often because the pain has reached an unbearable intensity that overrides their masking instincts, or because the condition has been progressing silently for weeks or months.

The Feline Grimace Scale (FGS): evaluating facial expression

Developed and validated by the veterinary anesthesia and welfare team at the University of Montreal, the Feline Grimace Scale (FGS) is the worldwide veterinary gold standard for evaluating acute pain in cats through objective facial cues.

The scale evaluates 5 Action Units (AUs), assigning a score of 0 to 2 points to each feature after observing the undisturbed cat for 30 to 60 seconds:

How to calculate and interpret the total score

• Add the scores across all 5 Action Units (maximum possible score: 10).
• Score 0 to 3: Baseline comfort or very mild discomfort.
• Score 4 or higher (≥ 4/10): Analgesic intervention threshold. Indicates that the cat is experiencing significant pain requiring medical examination and pain relief prescribed by a veterinarian.

Acute vs. chronic pain in cats

Pain manifests differently depending on its duration and underlying source:

1. Acute pain (sudden onset)

Arises from trauma, falls, post-surgical recovery, fight wounds, or sudden urinary blockage:

• Rapid, shallow, or abdominal-effort breathing.
• Wide, dilated pupils (mydriasis) even in bright light.
• Guarding of the affected body part and sharp defensive reaction if touched.
• Rigid, frozen posture—frequently crouched tightly in a corner.

2. Chronic pain (gradual and silent)

Frequently overlooked because owners mistake it for "just getting old." Chief culprits include feline osteoarthritis, feline tooth resorption (FORL), and chronic pancreatitis:

• Gradual withdrawal from interactive play and household activity.
• Hesitation or difficulty when jumping onto favorite furniture.
• Seeking secluded, dark, or ground-level hiding spots.
• Sudden grumpiness or swatting when petted over the lower back, hips, or joints.

Behavioral clues of feline pain in daily life

Beyond facial expression, changes in daily habits offer crucial diagnostic clues:

1. The hunched "meatloaf" posture

A comfortable, healthy cat sleeps stretched out luxuriously on their side or curls up loosely. A cat experiencing abdominal or visceral pain often assumes a hunched, guarded "meatloaf" pose: all four paws tucked tightly beneath the chest, back arched, head bowed low, and eyes half-shut for hours on end, unable to achieve restorative deep sleep.

2. Grooming changes: neglect vs. overgrooming

• Grooming neglect: Spinal, hip, or elbow arthritis makes contorting painful. The cat's coat becomes unkempt, dull, greasy, and matted over the lower back, tail base, and hindquarters.
• Compulsive overgrooming: When pain is localized (such as a burning bladder from cystitis or aching stifle joints), a cat may lick that specific area compulsively until the hair is stripped away, causing symmetrical alopecia or inflamed skin.

3. Litter box avoidance and accidents

When a previously tidy cat begins urinating or defecating just outside the litter box, the cause is often physical pain rather than a behavioral grudge:

• Stepping over high plastic litter box rims causes sharp hip or knee pain.
• Unstable, deep litter shifts painfully beneath arthritic toes.
• The cat associates the litter pan with the intense burning pain felt during a urinary tract inflammation episode.

4. Reluctance to jump and stiff gait

An arthritic cat rarely stops jumping overnight. Instead, they make subtle modifications: using an intermediate chair to reach the table, bobbing their head up and down while measuring the distance, or walking with stiff, unbending hind legs that lack shock absorption.

Why human painkillers are fatal to cats

Veterinarians consider this one of the most critical safety warnings in pet care: never give human medications to a cat.

1. The deadly danger of Acetaminophen (Tylenol/Paracetamol)

Cats have a genetic deficiency in the hepatic enzyme glucuronyl transferase, which is required to break down acetaminophen safely. In felines, the drug converts into a lethal toxin that damages red blood cells, converting hemoglobin into methemoglobin, which cannot transport oxygen. Within hours, the cat suffocates internally, their gums turn brown or blue, they suffer acute hepatic necrosis, and death occurs painfully. Even a crumb of a children's tablet can be fatal.

2. Ibuprofen, Aspirin, and human NSAIDs

Human nonsteroidal anti-inflammatory drugs have zero safety margin in cats. They cause rapid papillary renal necrosis, irreversible kidney failure, and perforating gastric ulcers with severe gastrointestinal hemorrhage.

Modern veterinary options for pain management

Feline medicine has advanced dramatically, offering safe, compassionate, and targeted pain relief:

1. Professional multimodal analgesia

• Feline-approved NSAIDs: Strictly formulated and weight-calibrated veterinary medications (such as meloxicam or robenacoxib), administered under monitoring of kidney and liver health.
• Gabapentin: An exceptionally safe medication widely used for neuropathic pain, osteoarthritis, and gentle pre-visit clinic sedation.
• Anti-NGF monoclonal antibodies (Frunevetmab / Solensia): A breakthrough biological treatment. A monthly subcutaneous injection that specifically neutralizes Nerve Growth Factor (NGF), relieving chronic arthritic pain without metabolizing through the liver or kidneys.
• Veterinary opioids: Used in clinical settings for severe acute trauma or post-operative surgical pain.

2. Home environmental accommodations

• Install ramps or carpeted steps next to beds and viewing perches.
• Switch to wide, shallow litter boxes with ultra-low entry lips.
• Raise food and water bowls slightly so the neck does not have to bend uncomfortably.
• Place orthopedic memory foam beds and self-warming pads in warm, quiet zones.

When to seek emergency veterinary care

Transport your cat to an emergency clinic immediately if you observe:

• Straining in the litter box with little or no urine produced (medical emergency; life-threatening blockage in males).
• Open-mouth breathing, panting, or labored abdominal respiration.
• Dragging the hind legs or sudden inability to stand (suspected aortic thromboembolism or spinal injury).
• Rigid, hunched posture with dilated pupils unresponsive to surroundings.
• Hard, swollen abdomen that provokes distress upon light touch.