A peeved tech
I agree with you, they should tell you if there are side effects. If I'm ever asked by an owner, I either tell them, or find out for them. A lot of times the vets even remind me to mention them when I take the prescription out to the client. However, if there were severe side effects that were common and/or worse than what we're trying to treat, we wouldn't use the drugs. We also try to mitigate side effects as much as possible, for example by running bloodwork before prescribing NSAIDS.
Also, the vet should also be reporting any adverse reactions. We always do, if for no other reason than that the company usually ends up paying for the treatment. In the 5 years that I've worked in clinics, I've only seen one truly horrendous drug reaction (ie not just swelling/vomiting/diarrhea, but full out organ failure) and the drug company paid all the bills to have the pet go to the vet college, see a barrage of specialists, and go through some expensive treatments. At the size of clinic I work at, we see about 50 pets a day and so seeing only one severe drug reaction in all the animals that have passed through here, I think that's pretty good odds.
Anyways, this is all completely off topic from what my original point was, which is treat with homeopathic or contemporary medicine, I don't care. As you are all quick to point out, there's more than one way to treat a problem so don't condemn a vet just because they're using the method that they know versus one that they don't.