The society said it hoped the Florida tragedy would spark reforms within the sport.
The criticism came as US polo authorities met to discuss reforms to better protect polo ponies.
A statement from the US Polo Association on the issue could be released within 24 hours.
Meanwhile, inquiries are continuing into the deaths of the ponies from the Lechuza Caracas team before a match in the United States Polo Open last Sunday.
A compounding pharmacy has released a statement admitting that the strength of one of the ingredients in the preparation was incorrect.
The Humane Society's director of equine protection Keith Dane said the group extended its condelences to those affected by the deaths.
"While news reports suggest that this may have been a case of accidental overdose of a toxic substance, this does not lessen the grief of those who cared for and loved these animals, and the American public.
"This tragedy," he said,"has brought to light the absence of drug policies and regulation within the sport of polo."
"There are no prohibitions or testing requirements for the use of drugs or other performance-enhancing substances.
"The HSUS calls on the authorities involved to continue to vigorously pursue this investigation and for the polo industry to use this tragedy as a catalyst to begin implementing reforms to ensure that policies are enacted and enforced that will ensure better protection for the horses in its care."