During two weeks in 2010, Fort Eustis police seized more than 10 types of the synthetic hallucinogen known as spice and charged more than 30 service members with related offenses.

Four years later, the statistics are quite different.

Drug tests administered to service members at Joint Base Langley Eustis have not detected a single case of spice usage since the federal fiscal year began in October. officials said.

"I think the message is getting out," said Bruce McFadden, deputy chief of drug demand reduction at Langley-Eustis.

Statistics kept by the Defense Department suggest that Langley-Eustis is not unique.

A 2012 study of a random population of soldiers, sailors and Marines estimated spice usage as high as 2.5 percent. That indicates spice usage was much more widespread than other illegal drugs. Consider that the overall rate of illicit drug use was 0.93 percent according to 2013 urinalysis tests.

Usage dropped off after legislation in 2012 banned several chemical compounds used to make spice. The rate in 2013 was estimated at .05 percent, said Joy Crabaugh, a Defense Department spokeswoman in the Personnel and Readiness Office.

Then in December 2013, the department officially changed its random urinalysis test to include spice. Estimated usage has ticked downward in the first four months of 2014, to .03 percent, Crabaugh said.

The substance "remains a serious health concern and poses a significant risk to both the safety and readiness of our force," she said.

At one time, it seemed the military was fighting an uphill battle against spice.

It had been sold legally over the counter as incense at shops that sell hookahs, which can be popular with service members returning from Iraq and Afghanistan. It gives users a high similar to marijuana or alcohol, but with dangerously unpredictable side effects, law enforcement officials and medical experts said.

Back in 2010, spice was not detectable in drug screenings.

That has gradually changed. Starting in early 2011, Navy commanders who wanted to screen their units for spice had to request it. Those results couldn't be used to directly discipline sailors because the Navy contracted with a private lab that didn't go through the same rigor as military drug labs.

Still, those tests helped quantify the problem, said Cmdr. Stacia Gawronski, Navy Region Mid-Atlantic staff judge advocate. The results could be used to revoke a sailor's security clearance, which is an administrative matter. That could lead to the sailor leaving the Navy.

"It wasn't ideal," she said. "I would say most people who popped on that, it would take a little bit longer. But I would say most of those people are probably not in the Navy today."

Naval Station Norfolk does not not track spice-related prosecutions, but Gawronski suggested the number of sailors using spice is relatively small.

"I think when spice first came out, sailors thought it was something they could lawfully use in the Navy," she said, "and I think it's very clear to them now that they cannot."

If the military is making headway, officials can credit not only advances in testing, but also some old-fashioned enforcement and — in the Navy's case — a push to change the culture.

A couple of high-profile cases in Hampton Roads sent a message that spice could end a career..

In 2011, 15 sailors from the USS Bataan were kicked out of the Navy for using or dealing spice. The next year, 13 sailors from the USS Mahan were disciplined for drug offenses, and all but one involved spice.