Hotboxing: What It Is, Why People Do It and Where It's Illegal

Roll up the windows, light a joint and let the smoke stay put. That is a hotbox, and smokers have filled cars, closets and bathrooms this way for decades, hoping the trapped smoke gets everyone a little higher.

The trapped smoke does reach everyone in the room, smokers or not. In a car on a public road, it also breaks the law for passengers as well as drivers in many legal states.

Key takeaways

• Hotboxing means smoking cannabis in a small, closed space, such as a car or a bathroom, so the smoke stays trapped.
• Non-smokers in a sealed-room study absorbed THC and felt some effects, and one screened positive at the standard 50 ng/mL cutoff.
• California, New York, Colorado and Virginia ban cannabis use in a car on public roads for passengers as well as drivers.
• In a 2022 living-room study, bong smoke pushed fine-particle pollution past the EPA's hazardous level, and it took hours to clear.
• A hotbox room at home is legal for adults in legal states, though a landlord or a hotel can often ban smoking.

Hot box, from railroads to closets

The word is older than the habit. Merriam-Webster dates hot box to 1848, when it meant a bearing on a railroad car that had overheated from friction, and the slang verb to 1994.

So what is hotboxing, in the cannabis sense? Merriam-Webster's answer is to smoke marijuana in a small, enclosed space, such as a car, in order to inhale the secondhand smoke trapped inside. A hotbox is also the space itself, which the same dictionary describes as an enclosed space filled with smoke, especially marijuana smoke. Hotboxing a car, windows up and vents closed, is the version most people picture. Indoors, it is usually a bathroom, a closet or a small bedroom with a towel along the bottom of the door.

Reasons people keep the smoke in

In our experience, people hotbox for a few reasons:

• A stronger high from the same amount of flower
• Privacy, or at least the feeling of it
• Cold or rainy weather that keeps the session indoors
• Group fun in a room too smoky to see across

Researchers have tested the first reason, at least for the people in the room who were not smoking.

Secondhand THC in a sealed chamber

In a study published in 2015, Johns Hopkins researchers seated six experienced cannabis smokers and six non-smokers in alternating seats inside a sealed chamber for an hour, while the smokers smoked joints at 5.3% or 11.3% THC. Extreme exposure like that can produce a positive urine test, the authors concluded, but positive tests are likely to be rare and limited to the hours right after exposure. Across that paper and two follow-ups from the same team, the main findings were:

• In the unventilated sessions, non-smokers reported feeling high and showed slight impairment on cognitive tests.
• Non-smokers had THC in their blood and oral fluid for up to 3 hours after a session.
• On urine screens, one non-smoker tested positive at 50 ng/mL, and several did at 20 ng/mL.
• Stronger cannabis meant more THC in the non-smokers, while ventilation cut their exposure sharply.

Even at its most extreme, the exposure mimicked active smoking, though to a lesser extent, the team wrote. So it is possible, though rare, to test positive for weed from secondhand smoke, and a closed-door hotbox comes close to the study's conditions. The chamber was about the size of a dorm room, Live Science reported. A car is far smaller, and we found no study that measured cannabis smoke inside one.

Potency pushed exposure up, and our own catalog runs well past the study's 11.3% THC. Gorilla Z, a GG4 and Original Z cross, lists 32% THC, nearly three times that, while Frozen Bananas Auto F1, a Frozen Bananas and BF Super Auto #1 cross, comes in at 22%. In our experience, the milder one is the kinder pick when a friend in the room is not smoking.

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Cars, public places and the law

The car is the risky part. So is hotboxing illegal? On a public road, yes, in every state in the table below, and passengers count too. California bars smoking or ingesting cannabis while riding in the passenger seat or compartment of a motor vehicle, on top of its ban for drivers, and its Vehicle Code makes either one an infraction on a highway. Four legal states spell out who is covered and what it costs:

A parked car is no loophole in New York, where the state's cannabis office says it is illegal for the driver or any passengers to smoke cannabis in a vehicle, moving or parked. Some states add a rule for kids. Oregon bans smoking in a car while anyone under 18 is inside, and its definition of smoking covers a lighted cigarette, cigar, pipe, weed or plant.

The driver faces a second risk. Driving under the influence of cannabis is dangerous and illegal, the CDC says, and in the Johns Hopkins chamber, non-smokers still had THC in their blood up to 3 hours later. A driver who never touches the joint still breathes the same smoke.

Outside the car, the usual limits apply. California also bars smoking cannabis in a public place or anywhere tobacco smoking is banned, and New York rules out private businesses such as restaurant patios, as well as hookah and cigar bars and federal property.

Smoke, particles and carbon monoxide

Trapped smoke is dense smoke. In a 2022 UC Berkeley study, researchers measured fine particles, called PM2.5, during eight bong sessions in a living room of about 215 square feet. Bong smoking produced 4 times greater PM2.5 concentrations than cigarette or tobacco hookah smoking, averaging 1,300 micrograms per cubic meter during the sessions. After 15 minutes, the level was already more than twice the EPA's hazardous threshold of 250, and 90 minutes after smoking stopped, it was still about half the peak.

The authors singled out hotboxing, writing that non-smokers are exposed to even higher concentrations during it. The CDC adds that secondhand cannabis smoke carries many of the same toxic and cancer-causing chemicals found in tobacco smoke, and that THC can pass to infants and children through it. In a Colorado study of 43 babies and toddlers hospitalized with bronchiolitis, a lung infection, from 2013 to 2015, 16% had a THC breakdown product in their urine.

Burning cannabis also makes carbon monoxide, which the CDC calls an odorless, colorless gas that kills without warning, and it can build up indoors. Fire is the other risk: smoking has long been a leading cause of home fire deaths, the U.S. Fire Administration says, and medical oxygen can explode if a flame or spark is nearby.

Setting up a hotbox room at home

At home, the law is friendlier. New York lets adults 21 and older consume cannabis in a private home or in most places where tobacco is allowed, and other legal states treat a private home much the same way. A hotbox room in your own place is legal, within two limits.

Landlords come first. In New York, a landlord cannot refuse to rent to a tenant who uses cannabis but can still ban smoking or vaping it on the property, and Michigan's 2018 law lets a lease ban smoking while protecting other ways of consuming. Hotels are the second limit. New York lets hotel owners ban smoking and vaping cannabis on their properties, so a hotel bathroom makes a poor hotbox.

In our experience, a safer hotbox room follows a short routine:

1. Pick a room in your own home, and check your lease for a smoking ban first.
2. Invite only adults 21 and older who want to be there, and keep kids and pets out.
3. Air the room out between rounds, since ventilation cut exposure sharply in the Johns Hopkins study.
4. Test the carbon monoxide alarm beforehand, and never smoke near medical oxygen.
5. Settle the ride home before anyone lights up, or plan for everyone to stay over.

A hotbox kept off the road

Hotboxing means smoking in a closed space so the smoke stays put, and that trapped smoke reaches everyone in the room, smokers or not. It fills the air with fine particles that take hours to clear, and in a car on a public road, it breaks the law for drivers and passengers in the states we checked. Keep the hotbox at home, short and adults-only.

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