Comment: Very easy.

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In reply to comment: Is this easy to get by chance? (see in situ)

Very easy.

Scopolamine is in Datura. It is a weed that is ubiquitious in Europe and the US. It is not common to see because it would be very inconvenient to use for self-defense and is a terrible "truth serum."

In my opinion, if you want to incapicitate someone without killing them, get some pepper spray or a taser.