Mints are edible, if you mean Mentha spp. And most all of them are edible, if you mean the mint family (Lamiaceae).
> Are all mints edible?
The essential oil of European pennyroyal (Mentha pulegium) is toxic and can kill ... but an essential oil is a single concentrated (very concentrated) constituent, and they're always iffy.
Avoid European pennyroyal and other mints with large amounts of pulegone in their essential oils -- if you're pregnant. If you're not, these true mints are somewhat relaxing and will help your cramps. They taste ghastly, though -- in other words, I don't like the taste of pulegone.
Avoid mints with large amounts of menthol in them if you're under, say, 2 years old: your liver can't handle the menthol. Which is why kids don't like the taste of menthol (found in various peppermints), and you get all sorts of disgusting artificial aromas in toothpastes for small kids instead.
Don't drink cups and cups of peppermint tea (Mentha x piperita) a day, as your bladder sphincter will give: you'll pee yourself when you laugh, when you cough, and when you jump -- and if you continue to do 10+ cups of peppermint tea a day, you'll soon enough pee yourself when you walk and talk. The problem corrects itself if you use your common sense and stop drinking so much peppermint tea.
Other than that, all true mints (Mentha spp.) are nontoxic. As far as I know. I use a lot of true mints.
As to mint family (Lamiaceae) plants: germanders (Teucrium spp.) contain livertoxic neo-clerodane diterpenoids. This wouldn't matter, as it's not used in herbal medicine -- but it's an adulterant for scullcap (Scutellaria spp.), and that matters. Skullcap is completely nontoxic, but it gets a bad rap because of the adulterant.
I haven't run across any other toxics in the family yet, and I use a lot of mint family plants as well: they're cool.
Related entries: YAMFAIs - Peppery mints - Peppermints - Sage types