Why mould multiplies the risks
Damp tea bags grow mould rapidly, often producing tremorgenic mycotoxins that attack the nervous system. These compounds work synergistically with caffeine—together, they lower the threshold for seizures in cats. The fuzzy growth you saw likely contained multiple mould species, some of which cause immediate gastrointestinal irritation while others target the brain.
Your cat's small size (4 kg) makes her especially vulnerable. Half a teabag's leaves could deliver 20–30 mg of caffeine to her system, nearing toxic levels even without mould. Add the fungal toxins, and her body faces dual assaults: one speeding up her heart rate while the other disrupts muscle control. The resulting twitches or stumbling may be misattributed to just caffeine when both are at play.
Timeline for mould-related symptoms
Unlike pure caffeine reactions that often begin within two hours, mould toxins can trigger vomiting within 30 minutes as the stomach rejects the irritant. However, neurological signs like dilated pupils or exaggerated reflexes may take 4–6 hours to manifest as mycotoxins reach peak bloodstream concentration.
This delayed onset creates a false sense of safety. Owners sometimes assume the worst has passed if their cat hasn't vomited immediately, only to face escalating crises later. Document every behavior change, even subtle ones like increased vocalization or refusing favorite spots—these help vets predict the next stages.
The teabag's hidden contents
Many commercial teas contain more than leaves. Flavorings like bergamot oil (in Earl Grey) or artificial sweeteners soaked into the bag during storage add separate toxic risks. Your description of 'mouldy' suggests prolonged dampness, which leaches these compounds from packaging adhesives or ink into the leaves themselves.
Check if the bag had staples, strings, or tags—cats often ingest these while chewing. Foreign bodies can cause intestinal blockages that mimic poisoning symptoms (lethargy, vomiting). Tell your vet about any missing pieces to determine if X-rays are needed alongside toxin treatment.
When home monitoring isn't enough
Certain scenarios rule out watchful waiting. If your cat has pre-existing conditions like hypertension or asthma, the cardiovascular effects of caffeine/mould demand proactive care. Similarly, kittens under six months lack adult liver enzymes to process toxins—what an older cat survives might overwhelm their underdeveloped systems.
Any fluid intake changes are red flags. Both increased thirst (from caffeine's diuretic effect) and refusal to drink (due to nausea) dehydrate cats dangerously fast. Skin tenting tests are unreliable in felines; instead, press a fingertip to her gums—if the white print doesn't pink up within two seconds, circulation is already compromised. This is an ICU-level emergency.
The full verdict, portion guidance and serving notes are collected on the Tea leaves & teabags food facts page.