Patent revoked after injunction: Can you claim compensation for lost profits?

When a company is barred from the market through summary proceedings based on a patent that is later declared invalid, the question arises as to who pays for the financial loss. Can the barred party recover lost profits based on ‘unjust enrichment’? In a ruling of 11 September 2025 the Court of Cassation ruled that this is generally not possible: despite the subsequent annulment of the patent, the decision in summary proceedings constitutes a valid legal cause for the enrichments

The facts and procedural background

This ruling revolves around a dispute between two pharmaceutical giants: Novartis (the patent holder) and Viatris (a producer of generic drugs).

The situation can be summarized as follows:

• The blocking: In 2010, Novartis obtained an injunction in summary proceedings against Viatris to place a generic drug (based on fluvastatin) on the Belgian market. The court ruled at the time that Novartis' patent was prima facie valid.
• The annulment: However, in 2011, following the summary judgment, the Novartis patent in question was finally revoked by the European Patent Office. As a result, the patent retroactively lost its legal status.
• The claim: Viatris claimed that it had lost revenue due to the unjustified injunction and that Novartis had made unjustified profits due to its monopoly position. Viatris claimed compensation based on enrichment without cause (unjust enrichment), since, in retrospect, the patent - the basis of the injunction - should never have existed.

The Brussels Court of Appeal rejected this claim, after which Viatris went to the Court of Cassation.

The decision of the Court of Cassation.

The Court of Cassation rejected Viatris' cassation appeal and upheld the reasoning of the court of appeal.

The core of the ruling rests on the following pillars:

1. Res judicata: A summary judgment is binding as long as it has not been overturned by another court decision. The fact that a judge on the merits later rules otherwise (or that a patent is overturned) does not eliminate the fact that the decision in summary proceedings was legally valid at the time of execution.
2. Valid cause: A claim based on unjust enrichment requires that there is no legal cause for the impoverishment/enrichment. The Court held that the res judicata decision in summary proceedings did constitute a valid legal cause. As long as that judgment existed, Viatris' blocking was legally justified.
3. Article XI.58 CEL: Although the Code of Economic Law (Art. XI.58) stipulates that the retroactive effect of a patent revocation does not affect previous decisions “without prejudice to the provisions on enrichment without cause,” this does not mean that such a claim will automatically succeed. The judge must still test whether all conditions (including lack of cause) are met.

Legal analysis and interpretation

Legal certainty over retroactivity

Annulment of a patent works ex tunc (retroactive effect): legally, the patent is deemed never to have existed. Viatris reasoned logically that if the right (the patent) never existed, then the measure based on it (the prohibition) had no basis either.

Nevertheless, the Belgian legislator deliberately put a brake on this retroactive effect with Article XI.58 CEL. The parliamentary preparation explicitly shows the fear that absolute retroactivity would endanger legal certainty. The Court of Cassation also follows this path and opts for the stability of the legal system. An injunction in summary proceedings creates an autonomous legal title. The fact that this injunction later proves incorrect due to new facts (the patent annulment) does not make its execution in the past unlawful or “causeless” within the meaning of the doctrine of enrichment without cause.

Distinction with fault liability

It is important to note that this judgment deals specifically with enrichment without cause (a quasi-contractual claim that does not require fault). The path to damages through fault liability (Art. 6.5 CC or Art. XI.58 CEL on “negligence or bad faith”) remains theoretically open. However, for that, the injured party must prove that the patentee knew or should have known that the patent was invalid, which is a much heavier burden of proof.

What does this mean for your business?

This ruling has significant strategic implications, both for patent holders and competitors (such as generic manufacturers).

• For the patent holder: You enjoy strong protection. If you enforce an injunction in good faith through the courts, you run little risk of later having to repay all profits through an enrichment action if your patent is still revoked. This lowers the threshold for actively enforcing your rights through summary proceedings.
• For the defendant: The risks are high. Are you blocked by a judgement in summary proceedings? Know that you will find it very difficult to recover damages for the period of the injunction, even if you are later proven right about the invalidity of the patent.
  • Advice: The focus should be on avoiding the injunction at the summary judgment stage itself, or appealing the decision as soon as possible, rather than counting on compensation after the fact.

Frequently Asked Questions (FAQ)

Is a patentee ever liable if his patent is subsequently found to be invalid?
Yes, but the bar is high. You must prove that the patentee was in bad faith or negligent (for example, by withholding information from the court). A claim purely on the basis that the patent has been revoked (strict liability or enrichment without cause) has little chance after this ruling.

Can I not have the summary judgment itself set aside?
This is very difficult when the deadlines for appeal have passed. A “revocation of res judicata” (an extraordinary remedy) requires specific grounds, such as fraud or withholding documents. The mere fact that the patent is later invalidated is usually insufficient in itself to overturn an earlier, final decision.

Does this ruling apply to areas of law other than patent law?
Although this ruling deals specifically with patents and Article XI.58 CEL, it confirms general principles about res judicata and enrichment without cause. The rationale that a judgment is a valid cause of action for enrichmentg may also be relevant in other commercial disputes.

Conclusion

With thisrulingthe Court of Cassation confirms the Belgian tradition of legal certainty. An executed judgment in summary proceedings constitutes a “legal shield” against claims of unjust enrichment, even if the underlying patent disappears retroactively. For companies, this underscores that the battle in court often has definitive financial consequences, regardless of the later administrative status of the patent.