AN 18-year-old is being held for questioning after being arrested at a Sandton house where Mandrax tablets with an estimated street value of R18m were seized at the weekend, Johannesburg police said. A Mercedes Benz, which was hijacked earlier, and other stolen goods were also found at the house. A police reservist patrolling the area spotted the luxury car, and on searching the house found nine boxes containing 450_000 Mandrax tablets.