"Coltsfoot" includes both Tussilago and the various species of Petasites.
They've been used as cough herbs. And both Petasites spp. and Tussilago farfara contain livertoxic PAs.
Trouble with livertoxic PAs is, they're insidious: you cannot detect their effects unless you do a liver biopsy (on live people) or a liver autopsy (after they died). Which is why people insist that "comfrey (Symphytum spp.) is perfectly safe - I've been eating it for years!" - oo-kay. So when was your last liver biopsy then? Any signs of VOD (veno-occlusive liver disease), the surefire sign of PA poisoning, and a disease that will slowly but surely do your liver in?
The livertoxic PAs are catalysts: a very tiny amount of livertoxic PAs will destroy a very large number of liver cells. Much like freons taking out the ozone layer.
It's a cumulative poisoning; eat coltsfoot, or comfrey, or Senecio, or one of the other plants which contain livertoxic PAs regularly or even irregularly, and watch the progress of VOD in your liver. You can't get VOD any other way, and if you do let it progress it means either a liver transplant or death, in the long run.
Of course we all die one day, but oh the irony, to die of a herb you use to stay healthy.
It's the "Well, aunty was poorly, may she rest in peace." -thing. So you didn't have a liver autopsy done, then? Of course you didn't - any fool could see that she wasn't well.
A hidden disease. Insidious.
I don't use any plants that contain livertoxic PAs.
Note, there's nontoxic PAs as well, so don't paint all plants that contain PAs with the same brush; but do avoid the ones with livertoxic PAs.
For safe cough herbs have a look at iceland moss, elecampane (there's a cool root!), mullein, plantago, horehound, thyme, hyssop, licorice ... there's lots.
Pretty much all of the Asteraceae (daisy family) and Boraginaceae (borage family) contain pyrrolizidine alkaloids. What you want to know is if they're toxic PAs.
They're toxic in most species of comfrey (Boraginaceae), and in the coltsfoots (be they Petasites or Tussilago) (Asteraceae).
They're nontoxic in the Echinaceas (Asteraceae).
And as far as I know, they're not toxic in boneset (Eupatorium perfoliatum), gravelroot (Eupatorium purpureum), or Joe Pye weed (Eupatorium maculatum) (Asteraceae).
Again as far as I know, they're toxic in the Ageratinas, which used to be Eupatoriums (Asteraceae).
And so on.
There are rumors that pyrrolizidine alkaloids could be destroyed by heat. I haven't heard anything definitive, and a lot of other alkaloids aren't destroyed by heat. The xanthine alkaloids, for instance: caffeine, theine, theobromine. And nicotine, from tobacco. Among others. So can you heat the coltsfoots and hope that they're then nontoxic? I have no clue, and no lab to test this with. I just avoid the coltsfoots.