Certainly not witt. The local carrier keeps a large quotient of the dosage at the site of application, thus mitigating the potential systemic sides of clenbuterol.
See this thread for some more info on the old school methods (with Lipoderm).
Lastly, this is a WELL timed question, as I just penned a blog entry about this very topic. It should be posted at www.avantresearch.com within a few days (our excellent technical staff is taking well deserved Holidays).