I don't really think they are, but like so many plants, they're likely an irritant and will probably make a muncher up-chuck. I've been really lucky so far - my kitties, who are just going on two this summer, haven't been interested in doing taste-tests (so far) of any Hoyas. Though I did recently get a small Spider Plant (after not having grown one in many years) and one of them managed to discover it and snacked on one of the airborn babies. But I think Spider Plants are close enough to grass that cats find them more appealing.

On the other hand, I used to grow a lot of Euphorbias (still grow the Crown of Thorn types...) and my last dog got ahold of one when he was a puppy. He didn't seem any worse for wear because of it (in spite of them having a reputation for being quite poisonous at worst, and a serious irritant at best...), but he died at about 8-1/2 with nasal cancer. I've often wondered if having gotten ahold of the Euphorbia as a pup might have started the ball rolling with that. Several years ago, I managed to rub my eye after working with a bleeding Euphorbia (thought I'd washed my hands well, but apparently not!) and had horrible pain for several hours in that eye. A year or so later, I suffered a spontaneous detachment of my retina (which the doc said was unusual.) I couldn't remember if it was the same eye, but again, it made me wonder...

I guess what I'm trying to say it's better to be safe than sorry, so I'd keep them out of their reach if your kitties are munchers.

Denise in Omaha

Plants from the milkweed (Asclepidaceae/Apocynaceae) are generally considered poisonous. The root of one species Asclepias tuberosa is commonly used as an expectorant and cough reliever in North American herbology and our common milkweed Asclepias syrica's new shoots have been cooked and eaten like asparagus. Asclepias curissavica the Mexican milkweeds caustic latex is used to remove warts.
Other plants from this family are used as food around the world including edible tubers of Raphionacme, Brachystemela and Fockea in Botswana Africa. Another milkweed Orthanthera jasminiflora is used in Botswana where the dried pods are used in cooking. Other milkweed relatives are also considered edible in Namibia. Brachystemela foetidum is one of the most commonly eaten milkweed relative, both the leaves and tubers are eaten.
This information comes from various articles in Asklepios which is the magazine of the international Asclepiad Society and A Modern Herbal Vol 1.

It would be safest to assume that the latex of Hoyas is toxic although it may not necessarily be dangerous. My dog often finds Hoya leaves and chews them but they are almost always dried and probably contain little latex unless they are eaten. I looked up common houseplant toxicity and Hoya carnosa was listed as non-toxic. There have been reported livestock deaths when hungry animals become desperate and eat milkweed leaves but the amount consumed was not mentioned.

Mike

All hoyas are nontoxic to cats...

Tish

Here is a link that might be useful: ASPCA

Thank you all so very much!!!!! I'm getting a couple of new, older rescue cats soon and have no idea what they munch on, if they do. I do know they are high energy guys.
It makes me happy to know I won't have to part with my hoyas.

Sande

That's one of the reasons I grow them - they're safe for pets!

Congrats on the upcoming new additions, Sande!

Kelly

Hmmm ... I'm not sure why cats should be immune to hoyas ... I guess they only eat a little bit to "give them a try" and then decide the latex isn't palatable and leave the plants alone.

Nonetheless, a word of warning: many Hoyas are poisonous to herbivores and this is well know where they grow naturally. Hoya australis is commonly removed and burned by farmers in Australia if they find it growing through shrubs or hedges, as cattle in particular will eat the nice fleshy leaves and then die. Animals that aren't indigenous to the areas where Hoyas grow in the wild aren't aware of the danger, whereas indigenous animals know better and leave them alone.

Tony