Article 54 EPC states that an invention shall be considered to be new if it does not form part of the state of the art. Based on this statement, you might initially consider that it is therefore not possible to obtain a patent for a substance that is already known. However, there are certain circumstances where the substance per se might be known but this does not preclude the patentability of such a substance.

Medical use of known substances  

Perhaps the most recognised example of the patentability of known substances comes in the form of a first or further medical use claim. More specifically, the Guidelines for Examination G-VI, 7.1 indicates that where a substance or composition is already known, it may still be patentable under Article 54(4) if the known substance or composition was not previously disclosed for use in a medical method. This means that if the substance or composition is known but not for use in a medical treatment, then it is possible to have a general claim to that substance or composition for therapy (i.e. as a first medical use).

Furthermore, where a substance or composition is already known to have been used in a "first medical use", it may still be patentable under Art. 54(5) for any second or further use in a medical method. For example, if the known substance has been discovered for the first time to be effective against cancer, then it may be possible to have a claim to that substance or composition for use in the treatment of cancer (i.e. as a second or further medical use).

Specific use of known medical treatment

The idea of being able to obtain a patent for a first or further medical use, was developed further in G2/08. In this decision, it was confirmed that where it is already known to use a particular medicament to treat a particular illness, Article 54(5) EPC does not exclude that this medicament be patented for use in a "specified new and inventive therapeutic application".

The examples given by the EPO of specified new and inventive therapeutic application, include new dosage regimes, new route or modes of administration and new classes of patients. However, this is not an exhaustive list, and other specific therapeutic applications may also be patentable.

Therefore, if a known substance for a known medical indication is found to be particularly effective when carried out using a specific dosage regime or on a specific subset of patient groups, then this may be patentable.  Singapore also appears to take a similar stance, where a novel dosage regimen is in principle considered to be patentable.

Specific combinations

A further possible allowable claim in Europe for a known substance is in the form of a specific new combination or composition claim. Such claims may take the form of a composition comprising substance A and substance B, where one or both substances may be known individually, but the combination has been disclosed for the first time. Of course, for such a combination to be patentable, it would need to not only be novel but inventive. In particular, such a combination may need to demonstrate an unexpected technical effect or synergy in order to meet the inventive step requirements.


Generally speaking, the EPO takes the view that a known compound is not rendered novel merely because it is available with a different degree of purity if the purity can be achieved by conventional means. The key phrase here is "by conventional means", where purification of a known substance is usually considered to be routine practice. However, if a given degree of purity cannot be obtained by conventional means, but rather new purification methods have to be developed in order to achieve this purity, then a claim to a known substance with a specified degree of purity may be patentable.


A chemical substance may take different crystalline forms, which are known as polymorphs. In the pharmaceutical industry in particular, different polymorphs can demonstrate different physical properties, such as bioavailability, solubility, hygroscopicity etc. Therefore, for some drugs, it may only be possible to obtain regulatory approval for a single polymorph. Accordingly, being able to obtain a patent for a specific polymorph for a known substance may be valuable for many drug candidates.

Whilst it is not by any means easy to obtain a patent in Europe for a specific polymorph, it is possible, if an unexpected advantage or property can be demonstrated. This was confirmed in T1422/12, where the claimed polymorph showed improved stability to epimerisation, which in turn resulted in improved biological activity. This increased biological activity was recognised as an unexpected technical effect and a patent was granted for the specific polymorph.

The key to successfully obtaining a patent for a specific polymorph therefore appears to depend on whether there is an unexpected technical advantage associated with that polymorph that could not have been predicted.

Selection Invention

A selection invention deals with the selection of individual elements, sub-sets, or sub-ranges, which have are not disclosed in the prior art.

A selection invention is considered to be novel if the selected elements are not disclosed in an individualised form in the prior art. Furthermore, whilst a selection from a single list in a given prior art document is not considered to confer novelty, if a selection from two or more lists of a certain length has to be made in order to arrive at a specific combination of features, then such a selection may be considered to meet the requirements of novelty (the "two-lists principle").

Examples of selection inventions include individual chemical compounds from a known generic formula and sub-ranges of several parameters from corresponding known ranges. A sub-range selected from a broader numerical range of the prior art  is also considered to be novel if the selected sub-range is a) narrow compared to the known range and b) the selected sub-range is sufficiently far removed from any specific examples disclosed in the prior art and from the end-points of the known range.

A selection invention must also meet the requirements of inventive step, where consideration must be given as to whether the skilled person would have made the selection or would have chosen the overlapping range in the expectation of some improvement or advantage. Generally speaking,  it is necessary to demonstrate an unexpected technical effect associated with the selection and the effect must apply to the entire range as claimed.


As illustrated above, even if a substance is known, there are plenty of possible routes that could be explored in order to obtain patent protection, whether this is via a new medical use, a novel combination, an undisclosed selection or a form of a substance which was not attainable previously (e.g. a polymorph or a substance with a high degree of purity).

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.