In certain cases, an adjuvant applied at a higher concentration may also be classified as an active substance. In such instances, an official EU authorization is required.
As of December 2025, the European Union has not yet established specific regulatory criteria defining the conditions under which a substance qualifies as an adjuvant rather than an active substance. Until such provisions are adopted, this assessment remains the responsibility of individual Member States.
A substance applied at a dosage of X L/ha may be considered an active substance in one crop, whereas in another crop—where a substantially larger spray volume is employed—it may be regarded as an adjuvant. Due to the significant dilution, the substance loses its efficacy as an active ingredient, although it may still fulfill a functional role as an adjuvant.
Consequently, the Ctgb evaluates substances based on the applied concentration. As a general guideline, informed by expert judgment, oils are typically used as adjuvants at concentrations of approximately 0.1%, whereas oils classified as active substances are applied at concentrations of at least 0.4%.
Other types of adjuvants (non-oil-based) are assessed on a case-by-case basis, relying on expert judgment. Applicants are expected to provide a substantiated rationale demonstrating that, at the proposed concentration, the adjuvant is highly unlikely to exert any effect as an active substance. This justification may include efficacy trials; however, such trials are not mandatory.