The USEF 2015 Drugs and Medications Guidelines have been published.

This year USEF has instituted a “12 hour rule” for therapeutic medications, and formalized withdrawal times for shockwave therapy and intra-articular medications.

-No injectable substances may be given within 12 hours of competition.
-Certain emergency exceptions apply if administered by a licensed veterinarian and a medication report is filed.

-Shockwave therapy may not be performed less than three days before competition.
-An exception exits for the treatment of back and sacroilliac
region. These areas may be treated by a licensed veterinarian up
to 12 hours before competition.

-No horse may receive intra-synovial injections (joints, tendon sheaths, bursas, etc. within 4 days of competition.
-for horses under two years old, the withdrawal is 30 days.

https://www.usef.org/documents/drugsMeds/2015/drugsmedsguidelines15_web.pdf