SAN DIEGO (AP) — U.S. troops are increasingly using an herbal mix called “Spice” that mimics a marijuana high and can bring on hallucinations that last for days.

Alarmed military officials have launched an aggressive testing programme that this year has led to the investigation of more than 1,100 suspected users.

So-called “synthetic” pot has become popular nationwide in recent years.

Two years ago, only 29 Marines and sailors were investigated for Spice. This year, the number topped 700. Those found guilty of using Spice are kicked out.

The Air Force has punished 497 airmen, compared to last year’s 380. The Army does not track Spice investigations but says it has medically treated 119 soldiers.

Military officials emphasize none was believed to be high while on duty.