The present invention relates to 1-(1-methylethyl)-4-{[4-(tetrahydro-2H-pyran-4-yloxy)phenyl]carbonyl}piperazine or a pharmaceutically acceptable salt thereof, in particular the hydrochloride salt thereof and crystalline forms of the hydrochloride salt to processes for the preparation of the compound or its salt to compositions containing it and to its use in the treatment or prophylaxis of neurological or psychiatric diseases, such as cognitive impairment, fatigue or a sleep disorder, for example in a mammal such as a human. The compound or a salt thereof has affinity for and is an antagonist and/or inverse agonist of the histamine H3 receptor.
