β-Agonists are used therapeutically in both human and veterinary medicine to dilate narrowed airways (broncholysis) in asthmatic respiratory diseases, to inhibit labor (tocolysis) and to treat peripheral circulatory disorders. They are also called β2-sympathomimetics or β2-adrenoceptor agonists. The use of β-agonists as fattening aids is prohibited in the European Union.

If β-agonists are applied, they can enter the organism and thus animal foods.

According to Council Directive 96/22/EC, the use of β-agonists as fattening aids is prohibited in the European Union.

In Regulation (EU) 37/2010, maximum residue levels are set only for clenbuterol for cattle and equidae. For all other β-agonists, no residues may be detectable in animal matrices.

For more information on the legal basis, please refer to the technical information.

The illegal use of ß-agonists as growth promoters in animal fattening and compliance with the limits for clenbuterol are monitored as part of the National Residue Control Plan (NRKP). Live animal stocks as well as animals on the occasion of slaughter are controlled so that traceability to the producer is guaranteed. As the NRKP serves the purpose of preventive consumer protection, sampling is target-oriented, taking into account knowledge of regional or local conditions and following up on indications or suspicions of unauthorized animal treatment.

In the Department of Veterinary Medicines, Hormones and Contaminants of the Institute for Food Safety Vienna, approximately 500 samples are tested for ß-agonists per year.

Mechanism of action and side effects

The action as a broncholytic is due to the fact that β-agonists cause bronchial muscle relaxation by stimulating β2-adrenoceptors. The only broncholytic agent commercially available as a veterinary drug is clenbuterol.

Its action as a tocolytic is due to the slackening of the gravid uterus and thus to the inhibition of labor, e.g., to prevent preterm birth. The most common tocolytic is clenbuterol.

At high doses, some β-agonists have an effect on the protein-fat ratio, favoring protein. Increased protein synthesis in muscle cells leads to increased muscle mass, making β-agonists interesting for use as growth promoters in animal fattening, which is banned in Europe, or as doping agents in humans. Clenbuterol in particular, probably the best known and most effective representative of this group of substances, has been and continues to be used illegally. However, the illegal use of other β-agonists is also known.

The typical side effects of β-agonists include tachycardia (palpitations), arrhythmias (cardiac arrhythmias), tremor (tremors), hyperglycemia (increase in blood glucose levels), and hypokalemia (decrease in blood potassium levels). Overdose increases all side effects, and life-threatening tachyarrhythmias may occur.

Legal regulation.

The use of β-agonists as fattening aids is prohibited in the European Union under Council Directive 96/22/EC. In Annex 1 of Delegated Regulation (EU) 2022/1644, β-agonists are listed under Group A (Pharmacologically active substances banned or not authorized for food-producing animals) as subgroup A1e.

Directive 96/22/EC was last amended by Directive 2008/97/EC of the European Parliament and of the Council of November 19, 2008, which did not affect the prohibition of β-agonists in animal production. Directive 2008/97/EC was transposed into Austrian law by the Hormones Ordinance 2009(BGBl. II No. 218/2009).

Regulation (EU) 37/2010 only sets maximum levels for clenbuterol for cattle and equidae. For all other β-agonists, no residues may be detectable in animal matrices.

Further legal documents:

Ordinance of the Federal Minister of Health concerning the prohibition of the marketing of medicinal products containing certain substances with hormonal or thyrostatic action or ß-agonists(Federal Law Gaz ette II No.229/2009).

COMMISSION IMPLEMENTING REGULATION(EU) 2021/808 of 22 March 2021 concerning performance criteria for methods of analysis for residues of pharmacologically active substances in food-producing animals and the interpretation of results and methods to be used for sampling and repealing Decisions 2002/657/EC and 98/179/EC.

Control of residues

In the Department of Veterinary Drugs, Hormones, Contaminants and Special Analysis(THKS) of the Institute for Food Safety Vienna, we test food for residues of β-agonists under the NRKP. We are also the National Reference Laboratory for these substances.

Analyses and investigation spectrum

The investigated β-agonists belong to the chemical group of substituted phenylethanolamines. The analyte spectrum is continuously extended. The matrices investigated are liver, urine, blood plasma and milk.

The analytical method used is high-pressure liquid chromatography coupled with tandem mass spectrometry(LC-MSMS).