Mandatory Drug testing?

So last post I mentioned I signed up not for the 1/2 marathon as planned for in October but the full marathon. Now some background. I'm fairly new back to running and most who I've talked to about this think it is nuts and wonder if I might have been consuming some non performance enhancing non prescription, non legal medication during the sign up process.  I'm still not convinced either way. I need some input from anyone who might have experience.  Here is my rational for the full not the half and a bit of background on me beyond what the rest of this blog explains. I have always thought of the marathon as a great fitness goal, a challenging achievement (the half most certainly is as well but isn't in my mind as out there or as motivating).  I have no time goal just to finish and I plan to continue training and doing the event using a run walk method, kind of a Jeff Galloway thing, google it if you aren't familiar.  I'm able to comfortably run over an hour and over 6 miles at this point and have been walking and then running since September though running is really since Jan in any consistent way. Finally if I get up in mileage later in the summer during the long runs and find it too taxing on the joints etc then I'm happy to shift into the half and run a full at some other point. Right now I have momentum and motivation and summer gives me the time to put in the miles. Happy to hear your thoughts!