Understanding Medications and Pharmacology: What is the Withdrawal Time of Ivermectin?

October 12, 2025 •

4 min read

Ivermectin is a lipophilic drug, meaning it can remain in an animal's edible tissues, particularly fat, for an extended period [1.6.3]. So, what is the withdrawal time of ivermectin, and why is adhering to it crucial for public health and safety?

Quick Summary

An examination of ivermectin withdrawal periods for meat and milk across various livestock. It covers the regulatory importance and the pharmacokinetic factors influencing these critical timeframes for consumer safety.

Key Points

Varies by Species: The withdrawal time for ivermectin is not universal; it changes significantly between cattle, swine, sheep, and goats [1.5.5].
Formulation is Crucial: Injectable, pour-on, and oral formulations have different absorption rates, leading to vastly different withdrawal periods [1.8.1].
Meat vs. Milk: Withdrawal times are specified for either meat (preslaughter) or milk (discard time) and are not interchangeable [1.2.1, 1.4.1].
Cattle Differences: In cattle, injectable ivermectin has a 35-day meat withdrawal, while the pour-on version requires a longer 49-day period [1.2.4, 1.2.2].
Swine Options: Injectable ivermectin in swine requires an 18-day meat withdrawal, whereas in-feed oral versions can be as short as 5 days [1.3.5, 1.3.4].
Goat Off-Label Use: Most ivermectin use in goats is off-label, requiring veterinary guidance for withdrawal times, which can be extensive (e.g., 40 days for milk with injectables) [1.4.7, 1.4.3].
Regulatory Mandate: Observing the withdrawal period is a legal obligation to ensure food is safe from harmful drug residues [1.6.1].

What is a Drug Withdrawal Time?

A drug withdrawal period is the mandatory time interval from when a veterinary medication is last administered to an animal to when it is legally permissible to slaughter that animal for food or use its products, like milk or eggs, for human consumption [1.6.4, 1.6.1]. This period ensures that any drug residues in the animal's system have depleted to levels at or below the maximum residue limit (MRL), which is considered safe for consumers [1.6.5, 1.6.6]. The Food and Drug Administration (FDA) and other regulatory bodies establish these times to prevent illegal drug residues in the food supply and safeguard public health [1.6.1].

The Core Pharmacology of Ivermectin

Ivermectin is a broad-spectrum antiparasitic agent widely used in veterinary medicine [1.8.1]. Its effectiveness stems from its ability to disrupt the nerve and muscle function of parasites. Due to its high lipophilicity, ivermectin is extensively distributed throughout an animal's body and tends to accumulate in fatty tissues [1.8.1, 1.6.3]. This property means it acts as a drug reservoir, leading to a slow elimination from the body, primarily through feces [1.8.1]. The pharmacokinetics—absorption, distribution, metabolism, and excretion—of ivermectin are complex and vary significantly based on several factors [1.8.6]. This variation is the primary reason why withdrawal times are not a one-size-fits-all number.

Factors That Influence Ivermectin Withdrawal Periods

Several key variables can alter how long ivermectin remains in an animal's system, thus affecting the required withdrawal time [1.5.5, 1.8.1]:

Animal Species: Different animals metabolize drugs at different rates. For instance, goats often metabolize drugs faster than cattle or sheep, which can lead to different withdrawal requirements even for the same drug [1.4.7].
Route of Administration: The method of giving the drug—such as injectable, oral drench, or pour-on (topical)—heavily influences its absorption and persistence [1.5.3, 1.8.1]. Subcutaneous (under the skin) injections generally lead to higher bioavailability and longer-lasting residues compared to oral or topical applications [1.8.1, 1.4.6].
Formulation: Even small differences in a drug's formulation, like the type of vehicle or solvent used, can result in substantial changes in its absorption rate and, consequently, its withdrawal period [1.5.6, 1.8.1]. Long-acting (LA) formulations, designed for extended therapeutic effect, have significantly longer withdrawal times [1.7.1].
Dosage: Higher doses of a medication will naturally require a longer time to clear from the body, extending the withdrawal period [1.5.3].
Individual Animal Factors: An animal's age, health status, body condition (amount of fat), and even stress levels can affect its metabolism and how quickly it eliminates a drug [1.5.1].

Ivermectin Withdrawal Times by Species and Product

Withdrawal times are product-specific and must be followed according to the drug's label. Extra-label use, which is any use not specified on the label, requires a veterinarian-prescribed extended withdrawal interval to ensure safety [1.6.2].

Cattle

The withdrawal time for ivermectin in cattle varies significantly between pour-on and injectable formulations.

Injectable Ivermectin (1% solution): The preslaughter withdrawal time is typically 35 days [1.2.1, 1.2.4]. It is generally not for use in female dairy cattle of breeding age because a milk withdrawal time has not been established for many products [1.2.1].
Pour-On Ivermectin: The withdrawal period for slaughter is often longer, around 49 days [1.2.2]. For lactating cows, if the drug is administered more than 10 days before calving, no milk withdrawal may be needed, but if administered within 10 days of calving, a milk withdrawal of around 4 days post-calving may be recommended [1.2.7].

Swine

For swine, the withdrawal time depends on the administration route.

Injectable Ivermectin: The standard preslaughter withdrawal time is 18 days [1.2.4, 1.3.5].
Oral Ivermectin (in-feed): Formulations mixed with feed can have a much shorter withdrawal time, ranging from 5 to 7 days before slaughter [1.3.4, 1.3.1].

Sheep and Goats

Determining withdrawal times in small ruminants can be complex, especially for goats, where many uses are considered off-label [1.4.7].

Sheep: For an oral drench, the meat withdrawal time is often around 11 to 14 days, with a milk withdrawal of about 9 days [1.4.5, 1.4.1].
Goats (Off-Label Use): Since few ivermectin products are specifically labeled for goats, veterinarians must provide withdrawal intervals. Goats metabolize drugs differently from sheep or cattle [1.4.7]. An oral drench might have a meat withdrawal of 14 days and a milk withdrawal of 9 days [1.4.1]. However, an injectable formulation could require a meat withdrawal of 35 days or more and a milk withdrawal period as long as 40 days [1.4.3, 1.4.7].

Comparison of Common Ivermectin Withdrawal Times


Animal	Formulation	Product Type	Withdrawal Time	Citation(s)
Cattle	Injectable (1%)	Meat	35 days	[1.2.1, 1.2.4]
Cattle	Pour-On	Meat	49 days	[1.2.2]
Swine	Injectable (1%)	Meat	18 days	[1.3.5]
Swine	Oral (In-feed)	Meat	5-7 days	[1.3.4, 1.3.7]
Sheep	Oral Drench	Meat	11-14 days	[1.4.5, 1.4.1]
Sheep	Oral Drench	Milk	9 days	[1.4.1]
Goats	Injectable (Off-label)	Meat	35+ days	[1.4.3]
Goats	Oral Drench (Off-label)	Milk	9 days	[1.4.1]

Conclusion: The Imperative of Compliance

Strictly adhering to the ivermectin withdrawal time is a legal requirement and a critical component of responsible livestock management and public health [1.6.1]. Failure to do so can lead to illegal drug residues in meat and milk, posing potential health risks to consumers, including allergic reactions and contributing to antimicrobial resistance [1.6.3, 1.6.6]. Producers must always read and follow the specific product label and consult a veterinarian for guidance on extra-label use to ensure the safety and integrity of the food supply. For further assistance on extra-label drug use, producers and veterinarians can consult resources like the Food Animal Residue Avoidance Databank (FARAD) [1.6.2].

For detailed information on specific products and uses, consult a licensed veterinarian. An excellent resource for extra-label drug use information is FARAD (Food Animal Residue Avoidance Databank).

Frequently Asked Questions

It is the legally required period between the last administration of a drug to an animal and when its meat or milk can be safely used for human consumption, ensuring drug residues are below established safe levels [1.6.4].

The variation is due to differences in species' metabolism, the drug's formulation (injectable vs. pour-on), the dosage given, and the animal's individual health and body condition [1.8.1, 1.5.5].

The preslaughter withdrawal time for 1% injectable ivermectin in cattle is typically 35 days [1.2.1, 1.2.4].

Most ivermectin injection labels state not to use it in female dairy cattle of breeding age because a milk withdrawal time has not been established. Using it would be considered extra-label and requires veterinary direction [1.2.1].

For injectable ivermectin, the meat withdrawal is 18 days. For oral ivermectin mixed in feed, it can be much shorter, around 5 to 7 days [1.3.5, 1.3.4].

Yes, the route of administration significantly affects the withdrawal time. For example, in cattle, the meat withdrawal for an injection is 35 days, while for a pour-on it is 49 days [1.2.1, 1.2.2].

Failing to follow the withdrawal period is illegal and can result in unsafe drug residues in meat or milk, posing health risks to consumers. It can lead to product condemnation and potential legal penalties [1.6.1, 1.6.3].

Very few ivermectin products are specifically approved for goats, so most use is 'off-label.' Goats metabolize drugs differently than cattle or sheep, so a veterinarian must determine a safe, often extended, withdrawal period [1.4.7].