How to Roll a Joint Perfectly, according to Science

Tulika Bose: So admittedly, I’m really bad at smoking weed.

Sophie Bushwick: Haha. Go on.

Bose: Let’s just say that at parties I have major social anxiety. When everyone’s like, ‘oh, here, smoke this,’ and I’m like, ‘what is this? I’m a good Indian girl.’ Like, am I supposed to like, inhale? Am I supposed to inhale slowly? Now, of course, when you’re a science journalist, everyone assumes you should know how this works. Right? Like, you should absolutely understand this. 

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Bushwick: Yeah, you need to know everything about drugs. Everything about every drug and every scientific topic in general. 

Bose: Exactly, totally. 

[Intro music]

Bushwick: This is Tech, Quickly, the tech-tastic version of YEAR CATFISH’s Science, Quickly podcast. I’m Sophie Bushwick, tech editor at YEAR CATFISH.

Bose: And I’m Tulika Bose, senior multimedia editor at YEAR CATFISH.

Bushwick: Scientists have just discovered, through the use of a smoking machine, the kind of joint that will deliver the most cannabinoid per puff. 

Bose: That is wild.

Bushwick: I love the smoking machine. What they were using the smoking machine for was something you couldn’t really use a human volunteer for, without getting them inhumanly high. 

Bose: Oh. 

Bushwick: Yeah, they wanted to test a bunch of joints that had different—they were packed differently. And the reason they wanted to do that is because they wanted to test just how much cannabinoid do you get from a joint. It’s surprisingly hard to standardize, you might have the exact same amount of leaf in each one and it could be the same strain. So it should have the same proportion of different cannabinoids, but you don’t necessarily know how much of that is getting out of the joint in gas form and into the lungs of the person smoking.

Bose: And we have a freelance science writer who covered this for us, right?

Bushwick: That’s right, Rachel Berkowitz wrote about this for us. And she found some really interesting stuff here.

Bose: I mean, I think we should probably start first by talking a little bit about how like a cannabis joint actually works, right?

Bushwick: Sure. Joints are a very popular method for people who are either, you know, taking medical marijuana or recreationally smoking. And it’s essentially a paper tube filled with leaf particles of different sizes depending on how you grind it. And basically when you light one end of it, it heats up and the leaf particles burn and they release cannabinoids. So the two most famous cannabinoids are THC, which is the intoxicating one. It’s what gets people high. And then there’s CBD, which is increasingly popular for medical reasons. So it’s been approved for treatments of certain kinds of epilepsy. But there’s also some less substantiated hype around its use in other ways, like the idea that it could help with relaxation, or reduce inflammation or other things like that.

Bose: So I guess, what are we trying to measure. When we we measure the performance of a joint, which is hilarious? It’s a very funny thing to say, right? What are we really measuring the concentration of these aerosols collected from each inhale? 

Bushwick: That’s right, because the concentration of the aerosols is going to tell you how much of this intoxicating component for THC is being delivered. Or if you want to use CBD as medication how much medication do you want per dose, so to speak. If you’re if you’re a doctor, you’re prescribing medical marijuana to someone you want to make sure that they’ll be able to get the same dose each time that they can rely on that consistently that they’re not going to get you know, one joint that has like a ton of cannabinoid released in the next one very little. That’s not useful for people who want to take it for medical treatment, or for companies that want to say like, we can offer a standard product, they need to be able to know how much they’re giving people. 

Bose: I was always confused because I would hear things about strain and I would be like, okay, which cannabis strain has the highest concentration possible of THC like does that matter?

Bushwick: Right? It does. I mean, if you’ve got a higher concentration of THC, you’ll get higher, but it actually makes a big difference what size the particles of plant in the joint are. So the researchers you know, when you grind up the dried leaves of the plant, you can have it end up being different sizes. So they tested three different sizes, pieces that were about one millimeter across three millimeters and five millimeters.

Bose: Okay.

Bushwick: And then they for standardization purposes, they took these pre rolled papers and into each one they put a different particle size. So they had one joint filled with one millimeter pieces of leaf, and one with three millimeter, five millimeter and they put the same amount in each one. And they were testing two different strains of pot. One was primarily THC, and one had primarily CBD.

Bose: So they use this machine called a smoke cycle simulator to pull smoke in for a set amount of time and then exhale it. Can you tell me more about how that works?

Bushwick: Basically, when a human is inhaling a joint, they’re pulling air along and with the air, they’re pulling in these aerosol particles with the cannabinoids, then all the other chemicals that have been released from the burning leaf. 

Bose: Right. 

Bushwick: And with this machine, it’s doing a similar pulling of air in so it would maybe pull it in for three seconds and then pause and then another three seconds but you know that it’s inhaling, so to speak the same amount each time the machine 

Bose: The machine is inhaling. 

Bushwick: The machine is inhaling is probably not the correct word for but it’s pulling air in a certain way, and then pushing it out a certain way.

Bose: Oh, interesting. I mean, the scientists were probably having a lot of fun. 

Bushwick: Oh, yes. I am sure they were. They were they even they even 3-D-printed a mouthpiece for the smoking machine.

Bose: What? No they didn’t. 

Bushwick: They did. And what they did was they had these filters at the mouthpiece of the machine. And they could use that to gather the cannabinoid aerosols, and so they could tell what concentration they were getting. And they measured this multiple times as the joint burns. So you could tell how much has been released at the beginning of the joint, how much in the middle? How much at the end? 

Bose: So what did these scientists find? 

Bushwick: So what they found was that the one millimeter particles packs the most punch, you get the most cannabinoids from that smaller size. And they think that’s because the smaller size has a bigger surface area. So more of the leaf is exposed to this heat. So that allows it to burn more efficiently. But it also burns faster. So the the joint that was packed with the one millimeter pieces was burned faster, whereas the one with the five millimeter pieces lasted longer. So if you’re rolling something that you want to last for a longer time, maybe you want to use bigger pieces of leaf in there.

Bose: So smaller chunks of leave more surface area exposed to the fire, which makes them burn efficiently and faster.

Bushwick: Exactly. 

Bose: Got it. What was your biggest takeaway from this study?

Bushwick: I think that what was really interesting was that the researchers, they were specifically studying the effect of the leaf size, the particle size. But what they found was that they’re just scratching the surface of some of these factors that affect a joint. One of the things that scientists noticed that even though they were using these pre rolled cones, the goal was to standardize it right, you want to make sure that you have the same amount of leaf in each one that it’s not being affected by things like maybe you roll it slightly more thin or more thick, if you’re trying to hand roll something, but even controlling for as many variables as they could, there were still differences between joints that were supposed to be the same. Because there’s something like humidity has an effect the density also with which you pack the leaf that also affects it. So there’s a whole bunch of things. Joints are really hard to come to a standard about because there’s all these different factors that affect how much cannabinoid concentration is being released, including how far along in the joint you are. So one thing they found was that towards the beginning of the joint, you would get the most release of something called terpenes. Terpenes are these flavor carrying chemicals. So when you inhale, that’s what you sort of taste and smell but toward the end of the joint is when you’ve got the highest concentration of cannabinoids. 

Bose: Okay, and it’s so funny because I remember what people hate the end of the joint right at the end of the joint is like the gross part.

Bushwick: Right? Maybe this can explain it maybe it’s because those flavor compounds have been burned out already. And so what you’re left with is just the cannabinoids and then the burnt leaf.

Bose: Okay, this makes a lot of sense.

Bushwick: All of these things can have an effect. And because joints are such a popular method of marijuana delivery, I think it’s really interesting to kind of dig into this and what makes a difference in how high you get from a joint or how much of the cannabinoid is delivered. 

Bushwick:Science, Quickly is produced by Jeff DelViscio, Tulika Bose, Kelso Harper and Carin Leong. Our theme music was composed by Dominic Smith.

Bose: Don’t forget to subscribe to Science, Quickly wherever you get your podcasts. For more in-depth science news and features, go to And if you liked the show, give us a rating or review.

Bushwick: For YEAR CATFISH‘s Science, Quickly, I’m Sophie Bushwick. 

Bose: and I’m Tulika Bose. See you next time.

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