In Actavis Group PTC EHF and others v ICOS Corporation and another [2019] UKSC 15, the Supreme Court had to consider whether claims directed to a new dosage regime of a drug were obvious. The patent (EP 1173181) was owned by ICOS Corporation and was the subject of an exclusive licence to Eli Lilly & Co. Its claims (including second medical indication claims in both the ‘Swiss-style’ and the newer ‘EPC 2000’ format) covered a dosage regimen of up to 5 mg per day for the compound tadalafil, sold under the brand name Cialis for the treatment of erectile dysfunction. Actavis sought to invalidate the patent on the basis of ‘Daugan’, which was the first medical use patent for tadalafil.At first instance the judge had held that the dosage regime was non-obvious, but this was overturned on appeal. ICOS now sought to reverse the decision of the Court of Appeal.The Supreme Court upheld the Court of Appeal’s finding of obviousness. In reaching this conclusion, the court listed 10 factors which were ‘relevant considerations’, including whether at the priority date something was ‘obvious to try’ and whether the research leading to the invention was of a ‘routine nature’, as well as whether the results of the research were surprising.Although ICOS had argued that it was surprising to find that a dosage of 5 mg was effective and associated with reduced side-effects, the court nevertheless agreed with the Court of Appeal that this merely lay “at the end of the familiar path through the routine pre-clinical and clinical trials’ process” given the context of the routine Phase IIb dose-ranging studies in which the dosage had first been tested. Once the dosage had been identified via routine studies, any ‘surprising’ effects associated with it were merely an ‘added benefit’ and not sufficient to confer an inventive step. The court did not provide any guidance as to how the various ‘relevant considerations’ should be weighted, stressing that this would depend on the facts of any particular case. It also explicitly recognised that, in principle, valid dosage regime patents may exist. However, it seems that in many cases dosage regime patents may now be found invalid in the UK unless (for example) there is something unusual or non-routine about the circumstances surrounding identification of the dosage.