I really don't like tansy. Common tansy and tansy ragwort are widespread in my area and extremely invasive and difficult to get rid of. Tansy ragwort is on the list of plants that must be controlled in my state.
I would avoid taking it internally. They both contain thujone which is toxic and causes seizures and liver damage in large doses. Smaller doses over time can have a cumulative effect leading to liver damage. There are many cases of cattle dying from eating tansy ragwort that was growing in their pasture. Usually animals don't eat common tansy, due to its strong odor, but it can cause the same issue.
For some odd reason, things considered invasive in most places just aren't here on the farm, and the tansy is one of them. It's been there since 1992 and I've never seen it anywhere else, on farm or off. But good to know it is invasive in other locales so people can make the choice.
That's interesting. We have a few large patches of it around our property and it's always trying to pop up in new places. Maybe it really likes our climate. I do see tansy in a lot abandoned or poorly maintained property around here.