Should I take the drug test before reneging?

pretty much title.
I don't want them thinking i reneged due to being on drugs.

Also is this a pretty good way to do it?“Thank you for the offer to join x Corporation.  I’ve received an exciting opportunity elsewhere and will have to regrettably withdraw my acceptance with X. I'm sorry to have to notify you at this time because I was looking forward to working at your company.

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