Almost all of the parameters evaluated were improved during the course of this study in 33 cats with stress-related signs. The behaviour of most of the cats improved after 15 or 30 days of L-theanine administration, leading to high owner satisfaction.

However, this study was open-label and did not contain a control group. Conclusions should therefore be taken with caution as owners/vets could have expected some sort of improvement during this type of trial. Still, the extent of the decrease in undesirable stress-related signs observed during the study in most cats is promising and suggests that L-theanine could calm and relax cats. Especially, some signs like inappropriate urinating, excessive grooming, hypervigilance, excessive demands of attention or panicking were improved as of Day 15. Irritability also decreased and cats were found to be more calm and gentle at the end of the study.

Among stress-related signs, inappropriate urination (whether due to excessive marking or inappropriate elimination) was probably the most bothersome for the owners and is one of the most frequent causes of consultation [24,25,26,27]. This type of sign is mainly due to a lack of adaptation to the environment or to the social conflicts a cat faces on a daily basis. Interestingly, inappropriate urination disappeared in 66% of the cats in this study, despite the lack of a specific behavioural therapy.

In cats (and dogs), many factors can induce stress-related behavioural signs [23,24,25]: an unpleasant experience during development, unsuitable living conditions and environment, bad relationships with owners or other animals, or pain and pathological conditions. Conflicts with the owners can create and help perpetuate unwanted signs, and the reverse can be true as well. Behavioural therapy can help owners understand and face the condition and adapt their behaviour or modify the cat’s environment in order to reduce feline stress. Instead of reprimanding the animal (especially in case of inappropriate urination or nervousness), the owner will be more understanding which in turn will help the cat. Although behavioural therapy is the mainstay of management of behavioural issues, pheromones, nutritional supplements or psychoactive drugs can also be prescribed to decrease anxiety [22]. In the current study, although no specific behavioural modifications were implemented, some basic behavioural therapy advice was given to the owners. It is possible that this advice contributed, at least in part, to the results obtained. We feel, however, that the important reduction in unwanted signs recorded in this study cannot be attributed solely to owners given the absence of specific behavioural advice provided by veterinarians. Further studies could be performed to assess potential additional or synergistic benefits of Anxitane® tablets over behavioural therapy alone.

Over time, it was found in this trial that most signs significantly improved as of Day 15. Since product tolerance was very good, a longer administration over 2–3 months could have helped reduce further unwanted signs still detected at 1 month in some cats, like aggressiveness or hypervigilance/tenseness/fear. Indeed, it is generally advised to carry on administration of a stress reducing product for a few months since effects can be seen only after 8 or 16 weeks of administration [13, 32].

In this study, L-theanine significantly helped improve the sleep and mood of cats but did not have the same impact on disturbed eating and drinking behaviours. Again, a longer administration could have helped reduce the issues but other concurrent ailments (endocrine or renal, for example) cannot be excluded and should be checked in case the behavioural signs persist.

Although no study describing the mechanism of action of L-theanine in cat is available, it is highly likely that it is similar to what was described earlier in laboratory animals (especially, an action on glutamate receptors and release of neuromediators) [4, 17, 19, 21]. More specifically, no sedative effect of L theanine has been previously reported in human, in rats, nor in dogs [2, 7, 8, 13, 14] .Therefore we expect that the effects observed in this study are due to a decrease of the stress level (and not to a sedative effect).

Thus, as in dogs [13, 14], L-theanine can be of value as an oral dietary supplement in cats, as it is safe and easy to give to individuals presenting with signs of stress (hypervigilance, mydriasis, rolling skin syndrome, excessive meowing, inappropriate elimination, etc.), in order to help them cope with changes in their environment.