PID 02027010 (Oystershell NV, Belgium) is one of the many nutraceuticals available for dogs and cats. It has been shown to have an impact on the behaviour of dogs and cats and is marketed as a complement or alternative to behaviour treatments. The standard dose rate is 0.5 to 1 ml/kg bodyweight (BW), and treatment needs to be for at least 3 consecutive days before there is an effect. Two studies were conducted to determine the safety of the product. The tolerability in dogs was assessed in a blinded, randomized, placebo-controlled study (Study 1). Twenty-four dogs (16 m and 8 f; divided into 4 groups of 6) were treated for 15 d with either a placebo (5x the labeled dose rate of PID 020270101) or 1x, 3x, or 5x the labeled dose rate for 15 d consecutively. Based on daily observations, body weight, clinical laboratory parameters, and clinical examinations, the product was well tolerated and did not cause any adverse events. Some changes in clinical laboratory chemistry were observed, but remained within normal ranges and were not considered clinically relevant. In Study 2, single high doses (5 and 10 ml) were tested in 3 cats (m and f; average weight of 5 kg) to assess safety and determine if single high doses could have an impact on behaviour. The 5 ml dose had no impact on behaviour and there were no adverse events. The 10 ml dose resulted in a mild sedative effect for approximately 2 h in two of the three cats treated. One cat had diarrhea after treatment. Based on these studies, the product was safe if used at the label rate. However, further work is required to confirm safety when used over longer periods of time. Also, reformulation would be required if a high dose for immediate effect is desired.