Periwinkle

Why periwinkle is one of the more serious garden toxins.

Yes — periwinkle is toxic to cats per the ASPCA, and seriously so. The ASPCA lists Vinca rosea (also called Catharanthus roseus — the modern botanical name — periwinkle, running myrtle) as toxic to cats, dogs, and horses. The toxic principle is vinca alkaloids.

The ASPCA verdict, verbatim — and notice how far the symptom list goes: Toxicity: Toxic to Dogs, Toxic to Cats, Toxic to Horses · Toxic Principles: Vinca Alkaloids · Clinical Signs: Vomiting, diarrhea, low blood pressure, depression, tremors, seizures, coma, death.

This is the chemotherapy plant

Periwinkle is the genus from which the cancer drugs vincristine and vinblastine are isolated. These compounds were a transformative development in oncology — vincristine remains a backbone of childhood leukaemia protocols — precisely because they're powerful disruptors of dividing cells. In medical use they're administered in controlled milligram-per-square-metre doses with careful monitoring.

A cat chewing periwinkle in the garden is getting the same chemistry in an uncontrolled dose. That's why the ASPCA clinical-signs list runs all the way from "vomiting" through "tremors, seizures" and ends with coma and death.

This is not the same risk class as buttercup (irritant) or pothos (mechanical oxalate). This is systemic neurotoxicity.

A note on the botanical name

ASPCA lists Vinca rosea. Modern botany has reclassified the species into a separate genus as Catharanthus roseus (Madagascar periwinkle), while Vinca now strictly contains the temperate-climate periwinkles like Vinca minor and Vinca major. Both genera carry the same alkaloid chemistry and both are treated as toxic. If you see Vinca, Catharanthus, periwinkle, or running myrtle on a label, treat it as the same warning.

What the toxicity actually does

Vinca alkaloids bind a protein called tubulin and prevent it from polymerising into microtubules. Microtubules are the cell's internal scaffolding — required for cell division and for transporting cargo along nerve axons. Disrupting them produces two main effects:

1. Antimitotic — cells that divide rapidly (bone marrow, GI lining, tumour cells) are hit hardest. This is the basis of the chemotherapy use.
2. Neurotoxic — nerve cells depend on microtubule-based axonal transport. Disruption produces tremors, neuropathy, and ultimately seizures and depressed consciousness.

In a cat ingestion, the neurotoxic effects dominate. Signs progress over hours: GI upset first, then weakness and low blood pressure, then tremors, then seizures in heavy exposures.

Apocynaceae family — the dangerous neighbourhood

Periwinkle sits in Apocynaceae, the dogbane family. This family is consistently bad news for cats:

• Periwinkle (this page) — vinca alkaloids. ASPCA toxic.
• Oleander (Nerium oleander) — cardiac glycosides. Deadly at small doses.
• Mandevilla / Dipladenia — toxic, related alkaloids.
• Plumeria / frangipani — toxic, irritant sap with related chemistry.
• Adenium / desert rose — toxic.

If you're identifying an outdoor plant and it has the milky sap and five-petalled flowers typical of Apocynaceae, assume toxic and verify the species before deciding what to do.

What to do if your cat ate periwinkle

This is one of the toxics where fast response matters more than at-home triage. The window for effective decontamination (induced vomiting) is short, and neuro signs progress over hours.

1. Call your vet or the ASPCA Animal Poison Control Center at 888-426-4435 ($95 consultation fee) immediately. Don't wait to see what happens.
2. Bring the plant name to the call — periwinkle, Vinca, or Catharanthus roseus. The case manager will know the toxin class.
3. Treatment is typically decontamination (induced emesis under vet supervision if recent), activated charcoal, IV fluids, and supportive care for any neuro signs that develop. There is no specific antidote — care is symptomatic.
4. Don't induce vomiting at home unless your vet directs it. Aspiration is a real risk in a cat that's already neurologically affected.
5. Bring a sample of the plant to the vet if you can — confirms the ID and helps the toxicology workup.

How periwinkle compares to other garden toxics

For a sense of severity:

• Lily of the valley, oleander, foxglove — same severity tier. Cardiac glycosides; any ingestion is a vet emergency.
• Periwinkle — same severity tier. Neurotoxic alkaloids.
• Clematis, buttercup — irritant tier. Painful but rarely systemic.
• Spider plant, catnip, creeping thyme — safe groundcover swaps.

For the full toxic landscape, see toxic plants for cats. For safe garden alternatives, see safe plants for cats.