Just enough? Eduardo Munoz/Reuters

Marijuana and relaxation have always had a bit of a funny relationship.

On the one hand, nearly half of cannabis users say that their goal is to relax. Yet many people are also familiar with the marijuana freak-out, or have seen a paranoid friend disappear from a party because they "just can't handle it, it's too much, man."

So what gives? The simple answer is that feelings of panic probably mean someone has had too much — especially if they pulled a Maureen Dowd and ate an edible without knowing what they were getting into.

Knowing how much is too much can be hard, and a new study published in the journal Drug and Alcohol Dependence shows just how easy it is to overshoot the target. The study investigates the amount of cannabis that can push someone from relaxed to anxious, and suggests that the quantity that helps people relax is actually pretty small.

Looking for the "Goldilocks" zone

Marijuana is dose dependent — the more someone uses, the stronger the effects. To figure out the ideal quantity for promoting relaxation, the researchers selected 42 volunteers between the ages of 18 and 40, all of whom were familiar with cannabis but not daily users. They split them into three groups, giving either a low dose (7.5 milligrams of THC, the cannabinoid in marijuana that's mostly responsible for the high), high dose (12.5 mg), or placebo dose.

FILE PHOTO -- People smoke marijuana on the informal cannabis holiday, 4/20, in Boston Thomson Reuters

Volunteers came for two sessions. Two hours after taking their dose, they had to engage in a stressful task. In the first visit, they prepared for and participated in a mock job interview while being videotaped, then were given a five-digit number and asked to repeatedly subtract 13. On the next visit, they were asked to talk about a favorite book or movie, then play solitaire.

"We found that THC at low doses reduced stress, while higher doses had the opposite effect," Emma Childs, an associate professor of psychiatry at the University of Illinois at Chicago and an author of the study, said in a press release.

People on the low dose reported being more relaxed than those on the placebo, and their stress levels dissipated more quickly after the tasks. But people on the high doses paused more in the job interview and reported the tasks to be stressful, challenging, and threatening.

Those differences, however, were just in how people perceived the events. Physical stress markers like heart rate, blood pressure, and hormone levels were equal for all groups.

So how much pot is that, exactly?

"The doses used in the study produce effects that are equivalent to only a few puffs of a cannabis cigarette," Childs said. In other words, a few hits of a joint or bowl is enough to hit the low dose. And just a few more hits could easily bring THC levels in line with the "high" dose.

As Christopher Ingraham of the Washington Post notes, The Cannabist has calculated the amount of THC people get from an average joint. According to a study cited in their analysis, an average joint weighs about .32 grams. They say that smoking half of that would give users 9 to 11 mg of THC, assuming that about the same amount of THC would just burn off. That's right in between the "low" and "high" doses used in the study.

The Cannabist's formula multiples the weight of the joint by the THC potency of marijuana to tell you how much THC you'd ingest. So in a .32 g joint with a 13% potency, you've got about 42 mg of THC. The low 7.5 mg dose from the study would therefore be 18% of that joint, and the high 12.5 mg dose would be about 30% of it. (It's worth noting, however, that exact calculations are hard since some will always burn off. Plus, some joints are a lot bigger, with another commonly cited average being about .75 grams.)

There's a long list of caveats to the results of this study, however.

First, the sample size was relatively small and therefore not representative of how everyone might react. People with more experience are more likely to tolerate a higher dose without getting nervous, and we also know that the mode of marijuana ingestion affects the high. (An edible high isn't the same as a smoked or vaporized high.)

Differences between marijuana plants further complicate things, since samples can vary dramatically and the stuff sold legally in state stores is usually far stronger than anything used in research studies.

Additionally, the tasks that the study participants were doing may have been particularly anxiety-provoking — so using cannabis in an easier setting may mean a stronger dose would be associated with less anxiety.

And finally, the study evaluated the effects of pure THC, but this may not give a full picture of how marijuana affects users. Other cannabinoids in marijuana, particularly cannabidiol (CBD), may have soothing effects that reduce anxiety and may assuage some of effects of pure THC.

Lingering questions aside, this research does demonstrate a couple of things. For one, it's easy to cross the line from the relaxing amount of marijuana to too much. And two, a lot more research on marijuana's anxiety-reducing effects is needed (something that scientists who study marijuana frequently point out).

"Studies like these — examining the effects of cannabis and its pharmacological constituents under controlled conditions — are extremely important, considering the widespread use of cannabis for both medical and non-medical purposes," Childs said in the press release. "Unfortunately, significant regulatory obstacles make it extremely difficult to conduct this type of research."