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American Cyanamid Principles

The American Cyanamid principles, established in the case of American Cyanamid Co v Ethicon Ltd (1975), are a set of guidelines used by courts in the UK to determine whether to grant an interim injunction. These principles are designed to strike a balance between protecting the rights of parties involved in a legal dispute and ensuring that the legal process is fair and just.


Principle 1 - Whether there was a sufficiently serious (substantial) matter to be tried

The court must be satisfied that there is a serious issue or question to be tried at the full trial of the case. In other words, the applicant must demonstrate that they have a reasonable likelihood of success on the merits of their case. This principle ensures that the injunction is not granted unless there is a genuine legal issue in dispute.


Principle 2 - Whether damages were an adequate remedy for the claimant if an injunction was not granted

The court should consider whether monetary damages would be an adequate remedy for the applicant if an interim injunction is not granted. If damages can adequately compensate the claimant for their losses, the court may be less inclined to grant an interim injunction. This principle recognises that an injunction is an extraordinary remedy and should only be used when necessary to prevent irreparable harm.


Principle 3 - If damages would not be an adequate remedy, whether the claimant would be able to give an undertaking in damages to the defendant

In many cases, the party seeking the interim injunction may be required to provide an undertaking in damages. This means they promise to compensate the other party for any losses suffered as a result of the injunction if it is later determined that the injunction should not have been granted. Undertakings in damages help protect the rights of the party against whom the injunction is issued.


Principle 4 - 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

The court should weigh the balance of convenience between the parties. This involves considering which party would suffer more harm if the interim injunction is granted or refused. The court aims to minimise the overall harm caused while the case is pending.


Principle 5 - If these factors were evenly balanced, the court should consider maintaining the status quo

If the factors above are evenly balanced, the court should consider maintaining the status quo, which means not granting the interim injunction and allowing the parties to continue their activities as they were until the full trial. This principle ensures that injunctions are not granted lightly and only when necessary to prevent harm.


These American Cyanamid principles provide a structured framework for courts to assess whether an interim injunction should be granted. They are intended to ensure that the court's decision is fair, reasonable, and balanced, taking into account the interests of both parties while safeguarding against irreparable harm.

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