Animal died of false treatment by his vet

A friend’s dog whom I also liked very much and sometimes took care of died lately. He did not seem to feel very well so we took him to the vet who found out that he had a problem with the thyroid gland and gave him pills for that. Without any description, just with the advise to give him ½ of a pill in the morning and he other in the evening. For some time he really seem to feel better, until all of a sudden he died of a heart attack. Researching the medicine on the internet ( unfortunately too late, but you always have confidence in the doctors until you had a bad experience ) she found out the following:
- Since these pills are kind of dangerous, the animals should have been examined thoroughly before they are given them.
- The medicine should not be given in any case to dogs who suffer from uncured problems with the suprarenal capsule ( which Fips did and the same doctor gave the advise to try to improve it by not giving him certain things to eat ); so even if she can’t remember all dogs she treats she could have just looked in his file....

- The dose he’s been given was much too high and maybe for a dog of a Rottweiler’s size, not for a Golden Retriever mix. ....

So people be careful which vet you're going to, there are also black sheep among them, and if he suggests a certain method of treatment, it would be better to research it on the internet before.