Legal Case Summary
American Cyanamid v Ethicon [1975] AC 396
Guidelines and the issues to be taken into account by the court for the grant of an interim injunction
Facts
The appellant was a company that held a patent for artificial absorbable surgical sutures. The respondent was a company that intended to launch a suture to the British market which the appellant claimed was in breach of its patent. At first instance, the appellant was granted an injunction preventing the respondent’s use of the type of suture at issue until the trial of the patent infringement. On appeal, the Court of Appeal discharged the injunction on the basis that the case for patent infringement was not made out. The appellant appealed to the House of Lords.
Issues
The issue on these facts was primarily the extent of any substantive claim necessary for the grant of an interim injunction. The House of Lords however, set out detailed guidelines with regards to how the courts should deal with the grant of interim injunctions in general.
Decision/Outcome
It was held that (a) it was not the courts’ role to consider conflicting evidence in respect of an interim application. This was a matter for trial. (b) All that was necessary at this stage was that the claimant should show that there was a real issue to be tried. (c) The court should consider whether damages were an adequate remedy for a claimant if an injunction was not granted. If so, an injunction would not be available. (d) If damages were not an adequate remedy, the court should then ask whether the claimant would be able to give an undertaking in damages to the defendant. (e) If it was considered that there was any difficulty regarding the availability of damages on either side, the court should consider the balance of convenience between the parties. (f) If these factors were evenly balanced, the court should consider maintaining the status quo. On the facts of this case, the balance of convenience lay with the appellant and the appeal was allowed.
Updated 21 March 2026
This case summary accurately reflects the decision in American Cyanamid v Ethicon [1975] AC 396 and the guidelines laid down by the House of Lords for the grant of interim injunctions. The principles described remain good law and are still routinely applied by the English courts.
However, readers should be aware of some important qualifications and subsequent developments. First, the courts have recognised that the American Cyanamid guidelines do not apply universally. Where the grant or refusal of an interim injunction will in practice determine the outcome of the litigation (for example, where a full trial is unlikely), the courts have held that a stronger merits threshold may be required: see NWL Ltd v Woods [1979] 1 WLR 1294 and Cayne v Global Natural Resources [1984] 1 All ER 225. Second, in cases involving freedom of expression and privacy, section 12 of the Human Rights Act 1998 imposes additional requirements: the court must have regard to the Convention right to freedom of expression, and relief that might affect the exercise of that right should not be granted unless the applicant is likely to establish at trial that publication should not be allowed. This effectively applies a higher merits threshold than the general American Cyanamid standard in such cases. Third, in employment cases and cases with a strong public interest dimension, different considerations may also apply. These qualifications are well established but are not addressed in the summary above, which focuses on the core guidelines from the case itself.
