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

With this ruling, the Court of Cassation resolutely opts for legal certainty and the stability of judicial decisions over the material truth that the patent was invalid. However, this position is not uncontroversial and places Belgium in legal isolation.

Criticism: is an interim measure really a final cause?

An interlocutory decision is by definition provisional. If the judge on the merits (or the EPO) later rules that there is no patent, and therefore no infringement, the provisional measure should logically lose its raison d'être, even for the past. The Supreme Court here applies procedural “res judicata” too absolutely, at the expense of the reality that the measure was unjustified in hindsight.

International isolation: strict liability with neighbors

A very different regime applies in our neighboring countries. In France, the Netherlands and Germany, the principle is that whoever executes a provisional measure does so at their own risk. Does the patent later turn out to be invalid? Then the patent holder must compensate the damage, without the injured party having to prove ‘fault. In those countries, it suffices that the ’title“ (the patent/prohibition) is subsequently found to be erroneous. With this ruling, Belgium maintains a system in which the victim of an unjustified prohibition is left out in the cold, unless he can prove bad faith.

Tension with European law (Mylan v. Gilead)

Moreover, the tenability of this Belgian ruling is under pressure from recent European case law. The EU Court of Justice ruled in Mylan v. Gilead (Jan. 11, 2024 - C-473/22) that the Enforcement Directive (Directive 2004/48) permits a system of liability for those who take wrongful action. More so, this ruling suggests that strict fault liability may not be required. Belgium's strict refusal to award damages after the nullification of a patent seems at odds with this.

What does this mean for your business?

Despite criticism, this ruling is the law in Belgium today. This has significant strategic implications, both for patent holders and competitors (such as producers of generics).

• For the patent holder: You enjoy exceptionally strong protection in Belgium. If you enforce an injunction through the courts in good faith, you run little risk of having to repay all profits later through an enrichment action if your patent is killed. This lowers the threshold for actively enforcing your rights through summary proceedings. Note: due to European developments, it cannot be ruled out that in the future judges may still be pushed towards strict liability via preliminary questions to the Court of Justice.
• For the defendant: The risks are higher in Belgium than in neighboring countries.
  • Prevention is crucial: You must fight the injunction in summary proceedings with all your might. Claiming damages afterwards is quasi-impossible.
  • Safeguards questions: In the summary proceedings, try to demand that the patentee provide a security or guarantee (as may be possible in the UK or in seizure proceedings), which can serve as compensation if the patent is later invalidated.

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.

What if I can prove that the other party knew their patent was weak?
If so, you do stand a chance. The ruling excludes damages based on fault liability (negligence or bad faith) is not out of the question. However, the threshold is high: you must prove that the patentee acted negligently in seeking the injunction, not just that the patent was revoked.

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.

Is this ruling final or is there still an appeal?
This is a Court of Cassation ruling, which means that the discussion in this case is nationally closed. However, given the tension with European law (Mylan t. Gilead), in future litigation, parties could seek review of Belgian rules through the Court of Justice of the EU (CJEU).

Why does Belgium differ so much from the Netherlands and France?
This is due to a strict interpretation of Article XI.58 CEL and our procedural rules around ‘res judicata. Whereas our neighbors focus on the fact that the executor of a judgment bears the risk (’strict liability“), Belgium focuses on the formal validity of the court decision at the time of the judgment.

Conclusion

With this ruling, the Court of Cassation confirms the Belgian tradition of legal certainty. An executed summary judgment constitutes a “legal shield” against claims of unjust enrichment, even if the underlying patent disappears retroactively. Belgian jurisprudence is thus pursuing an idiosyncratic course that poses significant financial risks for companies.