Can you really get a secondhand high or contact high?

Whether you're familiar with the term secondhand high, contact high, or contact buzz, the theory is the same: exposure to secondhand weed smoke may cause someone to be involuntarily stoned and even fail a drug test. The prospect of feeling high unintentionally is alarming, to say the least, but is this theory true?

If you're looking to know whether secondhand cannabis smoke can enter your system or if you'll ever be able to attend a Grateful Dead tribute concert without getting blazed, this is the guide for you.

Is it possible to get a contact high?

As with many things weed, the answer is both yes and no according to a 2015 Johns Hopkins University study.

Researchers started with a dozen people, six of whom were cannabis smokers and six who were non-smokers. In the first experiment, all 12 subjects spent an hour together in a small unventilated room, during which time each smoker puffed through 10 joints, each with a THC content of 11.3%. Afterward, the non-smokers reported feeling pleasant, more tired, and less alert. And sure enough, their blood and urine tests came up positive for THC.  

The second experiment repeated the scenario, but this time in a room with ventilation. The non-smokers in this experiment later said they felt hungry, but none of them tested positive for any noticeable amount of THC. (To be fair, the study did also finish up around lunchtime.)

Researchers concluded that being exposed to marijuana smoke under “extreme conditions” like a tightly packed, unventilated area can indeed give non-smokers a contact buzz. Outside of that very limited scope, any contact high you think you might be feeling due to secondhand cannabis smoke is likely a result of the power of suggestion.

You can't get high from catching a whiff of someone's joint while walking down the street, but you will feel some effects if you are sitting in an unventilated enclosure filled with smoke. Some people do this intentionally, and those people call it hotboxing.

Bottom line: if you spend a lot of time in a small room with the windows sealed shut while your friends are smoking, your blood and urine might test positive for THC and you may feel its intoxicating effects. But outside of a hotboxing hostage scenario, it's more likely your contact high is all in your head, so to speak.

women smoking joint outside
It takes some concerted effort to get a real contact high. 
Photo by: Gina Coleman/Weedmaps

Is THC active after cannabis smoke is exhaled?

If we pull a page from the 1999 British Journal of Anesthesia, we learn that the lungs absorb most of the THC when cannabis smoke is inhaled. Researchers have discovered that approximately 50% of THC and other cannabinoids present in cannabis make it into the smoke and are inhaled.

“Experienced smokers, who inhale deeply and hold the smoke in the lungs … virtually all of the cannabinoids present in the mainstream smoke enter the bloodstream,” the report reads, leaving very little THC in the surrounding air to be inhaled and absorbed by a passive inhaler.

In order to get a secondhand high, you would need to be in an unventilated room for some time to feel anything. Otherwise, the cannabinoids will have disappeared into the air before ever reaching you.

Bottom line: studies show you would need to be in an unventilated room for some time to feel a legitimate contact high. More than likely, though, the cannabinoids will have disappeared into the air before ever reaching you.

What does it feel like to be high?
Avoid a contact high from secondhand marijuana smoke by cracking a window.
Photo by: Gina Coleman/Weedmaps

Are there any other studies on secondhand highs?

Studies performed during the mid-to-late-1980s investigating the mystery of the secondhand high determined that the acute toxicity of cannabis was extremely low, therefore making it difficult to feel the effects without direct inhalation. While their conclusions may still apply, cannabis has changed over the years and the studies may need reexamination.

The potency of THC-dominant cannabis has increased as cultivation techniques and technologies have advanced. In the early 1970s, the average joint contained roughly 10 mg of THC, whereas a modern joint may contain 60-150 mg of THC or more. The THC potency in today's marijuana flowers is far greater than the weed from the 1960s and 1970s, therefore much of the early research produced from studying secondhand highs may be outdated.

While there's an abundance of research demonstrating the adverse health effects of secondhand exposure to cigarette smoke, there is little evidence to suggest that secondhand marijuana smoke carries the same detrimental health risks as tobacco smoke. Considering that past research has found marijuana smoke to be less carcinogenic than cigarette smoke, there doesn't seem to be an immediate public health concern regarding the effects of secondhand weed smoke.  

Bottom line: the research may be outdated, but as long as you're not stuck in a poorly ventilated room during a heavy smoke session, you shouldn't be concerned about feeling stoned or having THC enter your system.  

Frequently asked questions

Can you get high walking through the remnants of secondhand weed smoke? 

No. It's highly unlikely you'll experience a secondhand high or have cannabis byproducts show up on a drug screening if you pass by some dissipating marijuana smoke. As the 2015 Johns Hopkins University research shows, in order to catch a secondhand high, you'd have to be under extreme conditions that lack proper ventilation. 

contact high from smoke
Don't expect to get a contact high from walking through some dissipating marijuana smoke.
Photo by: Gina Coleman/Weedmaps

Nonetheless, weed smokers should still be respectful of people who don't consume cannabis. The next time you spark one up, try to be aware of your surroundings and make an attempt to keep the smoke and strong odor away from non-smokers. To enjoy a smoking session without affecting non-partaking neighbors, cannabis users should spark up in well-ventilated areas to ensure passive inhalers will not feel the effects of the smoke or test positive for weed. 

Can you get high from smelling weed?

Since it's difficult enough to get a contact high smelling marijuana smoke, it's 100% impossible to get high from smelling weed in its raw or cured form. However, you may feel some barely-there, calming effects or the faintest whisper of energy after deeply inhaling some terpene-rich weed. 

linalool terpene
Lavender and some types of weed may be rich in the terpene linalool, but smelling them will not give you a contact high.
Photo by: Gina Coleman/Weedmaps

Terpenes are the compounds that give all kinds of plants — including marijuana — their aroma and flavor. In the same way you may feel a subtle increase in focus after smelling lemons, which are rich in the terpene limonene, or some calming effects after smelling linalool-rich lavender, you may simply feel happy smelling good weed. But high? Absolutely not. 

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The information contained in this site is provided for informational purposes only, and should not be construed as medical or legal advice. This page was last updated on March 23, 2021.