DMDENVER  - Students have found a new way to sneak marijuana into schools by using vapor pens that allow them to smoke without giving off the drug’s distinctive smell.

Since Colorado legalized the drug, school administrators have had to fight back against students who finding creative ways to get high during class. Edibles and inhalers that have been turned into makeshift bongs were two of the first ways that caught on, but now vapor pens are causing a more difficult problem because they are the most discrete. The pens, sold for upwards of $25, were initially used for cigarette smokers but now people can buy tablets of marijuana oil to place in the pens.

‘I’ve seen people in my math class and they’ll be sitting there with the teacher and they’ll be smoking it and they won’t even know,’ said Lakewood High School student Jack Maestas. The plastic around the capsule is melted by the water in the pen and the user inhales a whiff of the result from a small mouthpiece at the end of the pen. When vapor pens are used by cigarette smokers, they insert a capsule of liquit nicotine as opposed to tobacco. Because the water mixes with the oil, the smell normally associated with the drug is dilluted to a point that it isn’t noticeable.

The only possible tip off for teachers comes when some users exhale the vapor back out of their mouths, but that only lasts a second making it tough to pin down. Principal Ron Castagna told CBS Denver that teachers have been clued into the trend and are keeping an eye out for any suspicious activity.

‘The nervous habit of biting on your pen has a new meaning to it,’ Mr Castagna said. The trend is being helped by a prevalence of YouTube videos that show people demonstrating how retool vapor pens for marijuana, showing ways to keep the smoke controlled while using it during class.