Back to Top


Whenever a drug is used in animals, there is a potential for drug residue in edible tissues and other foods consumed by humans. Edible tissues and food products include muscle, liver, kidney, fat, skin, milk, eggs, and honey.

Human health effects of drug residues in foods include:
  • Acute allergic and toxic reactions. As an example, it is estimated that 1 in 10 people are allergic to penicillin. Residue exposure in the population can have a range of reactions from a rash to anaphylaxis.
  • Chronic reactions due to long-term, low-level exposure, as can happen from continued ingestion of mercury-contaminated fish.
  • Antimicrobial resistant pathogens may develop from inappropriate use of antimicrobials, which could potentially be transmitted to consumers.
How do we protect consumers from drug residues?
Before a company can bring a livestock drug to market, it must have undergone a rigorous drug approval process and submitted data to the FDA that shows the drug is safe and effective for the animal, safe for the environment, and safe for consumers when used according to the label. The tolerance is the legally allowed concentration of a drug residue, established for individual tissues or other food products. Once a tolerance is established, a withdrawal time can be determined. Tolerances for livestock drugs are established by the FDA, while tolerances for livestock pesticides are established by the EPA.
Withdrawal Time
Withdrawal time is the period of time from when a drug is administered to when the drug concentration falls below the tolerance. Every approved livestock drug has a withdrawal time, which only applies when the drug is used according to the labeled directions. Having a labeled withdrawal time does not mean there will be no drug residue in the edible tissue or food product. It means that if there are residues, they will be at or below the established tolerance level.
If a drug is used in any manner different from the label (ELDU), the withdrawal time is affected. For example, if a higher than labeled dose is used, it can dramatically change when the residue concentrations fall below the tolerance. Because of this, the only way a drug can legally be used extra label is when it is prescribed by a veterinarian, who must also issue an extended withdrawal interval.
An Extended Withdrawal Interval must be scientifically based. A veterinarian may contact FARAD with questions regarding withdrawal interval of drugs when used extra label. FARAD has also developed a Withdrawal Interval Lookup Tool which provides FARAD recommended withdrawal intervals for selected extra label uses of a limited number of drugs.