The Metropolitan Police Department said Tuesday that it arrested a 41-year-old assistant police inspector on Monday on suspicion of consuming 0.3 gram of amphetamine.

The arrest was made after the suspect, Masayuki Higo, an assistant inspector based at Tokyo's Takanawa Police Station, reportedly confided to a former colleague and supervisor that he had mixed 0.3 gram of amphetamine with water and consumed it.

Higo, who reportedly has trouble sleeping, made the phone call to the former supervisor's home Friday night, a day after he was told by doctors that he should check into a hospital for treatment, the police said.

Higo reportedly told investigators that he had bought amphetamines twice in the past month in Tokyo's Shibuya area from street vendors.