In the UK, Ketamine is not a controlled substance under the Misuse Of Drugs Act. This does not make it a legal high. It can only be obtained by a doctor's prescription. So if you were arrested with Ketamine, you could be prosecuted under the Medicines Act for supply without a licence.

UK police have had some success prosecuting under "conspiracy to offer to supply MDMA" laws.

in the US
In August 1999, after a high profile campaign and its demonisation as a 'date-rape' drug, Ketamine became a Schedule III controlled substance in the United States, federally illegal to possess without a licence or prescription. (1)

1. Ketamine: Dreams & Realities p. 39