Someone sparks up a joint and someone else leaves the room. We all have this friend. They worry about getting a contact high; secondhand smoke making them stoned. But is getting high from secondhand cannabis smoke a legitimate concern? Some folks assume that they will catch a non-participatory buzz from just being in the same room as a sesh. Additionally, some also believe that one can fail a drug test without ever consuming cannabis. How reasonable are these worries? Let’s look at the science behind whether or not a contact high can actually occur from secondhand exposure to cannabis.
The Secondhand Smoke Study
A contact high occurs when a sober individual experiences mental or physical changes after exposure to secondhand cannabis smoke. While there is very little research surrounding this topic, here is what we know. The most relevant experiment to date is from researchers at the John Hopkins University School of Medicine who conducted a study in 2015. Its focus was to determine the effects of lingering smoke from cannabis on subjects that never intentionally consumed it. The study was divided into two separate sessions, one in a non-ventilated room and another in a ventilated room. Each session had 12 participants; six chronic smokers and six non smokers.
The Set Up
For each 1 hour session, the participants sat in a Plexiglass room around a table. Imagine a living room with a low ceiling (10ft x 13ft x 7 ft) . Smokers and non smokers sat in alternating positions around the table. This was to keep the distribution of smoke as even as possible. The researchers gave each smoker ten 1 gram joints. They told them to smoke as much or as little as they wanted. Participant blood, urine, heart rate, motor skills, cognitive performance and subjective effects were then measured after each session. Here is what they found.
Results from Non Ventilated Session
In non-ventilated conditions, secondhand cannabis smoke exposure produced detectable levels of THC in both blood and urine for all of the non smokers. Subjective effects such as “feeling high” or “having the munchies” were notably higher compared to the baseline. Cognitive and motor abilities also decreased significantly. Most measured effects returned to pre-session levels within 4 hours.
Side note – the six (chronic) smokers puffed down a total of 14.4 grams during the non-ventilated session in just one hour. Just over a half once was clouding that room! The Plexiglass “chamber was visibly very smoky during the unventilated sessions [and] became difficult to see through the opposing wall clearly.” It’s no surprise that non regular cannabis smokers were getting baked in that hotbox.
Results from Ventilated Session
In the ventilated session, results were markedly different. Only 4 of 6 non smokers showed detectable levels of THC immediately following exposure and none were detectable within an hour. There were “no significant effects on heart rate or blood pressure.” The only subjective effects that were noted were “hungry/have munchies,” but even the researchers interpreted this as unrelated (it was getting close to lunchtime). Finally, motor and cognitive abilities in the non smoking group actually increased slightly compared to their baseline.
The study does suggest that the conclusions from this experiment could be different from real life scenarios. For example, how often would a non smoker sit in a half ounce hotbox for an hour (maybe that’s what happened to Ross Rebagliati)? However, the differences in effects between the ventilated and non ventilated rooms are worth noting. A non smoker exposed to cannabis in an area with normal ventilation is likely to experience either minimal or no detectable effects.
It’s safe to say that contact highs are real, but the risk of them occurring isn’t quite as substantial as some may believe.