Ceci n’est pas la marijuana…

“You have been assigned to the condition to smoke an active marijuana cigarette that contains THC. THC is the primary psychoactive cannabinoid that gets people high.”

Does the fact that you are told you are taking a drug effect your reaction to that drug… or the drug’s effect itself? This was the simple question posed by a group of researchers publishing in Psychopharmacology. The effect of taking a drug is one thing. The effect you expect it to have is something altogether different.

“…users believing they are smoking marijuana may compensate for expected intoxication effects when engaged in deliberate decision-making by making less impulsive and risky decisions.”

34 subjects at a time were given the task to smoke a cigarette that contained marijuana or a cigarette that contained a placebo. Participants were selected based on an interesting set of criteria; native English speakers, 18 to 30 years of age, frequent marijuana use over the past month (at least once a week and at least ten times in the past 6 months), and self-reported ability to abstain from marijuana for 24 h without withdrawal.

This was a balanced placebo design experiment, examining the relative effects of expecting to receive active marijuana. These regular marijuana smokers, randomly assigned into one of four groups:

  • Told they were getting THC but got a placebo

  • Told they were getting THC and got THC

  • Told they were getting a placebo but got THC

  • Told they were getting a placebo and got a placebo

All rather deceitful and standard practice for a placebo trial.

What came next was probably the most regimented smoking session the participants had ever undertaken. Smoking sessions occurred in a 75-square-feet ventilated smoking room, with standard-issue humidified cigarettes that are rolled at both ends. And smoked according to the “standardized paced puffing procedure” — until the ash reached a mark 10 mm from the end.

Subjects and participants were then evaluated for subjective intoxication, behavioral impulsivity, and decision-making related to risky behaviours.

The laboratory test known as the Stop Signal Task is one commonly employed as a laboratory measure of inhibitory control. In essence, it uses an external stimulus to signal participants to interrupt or inhibit an already-initiated motor response. Simply put, subjects are asked to respond as fast as they can to symbols on a screen. Then an auditory tone tells the participant that they are to try and withhold their response to the current symbol on the screen. The tone occurs occasionally, in an unpredictable way, and at various latencies after the appearance of the letter on the screen. The stop signal reaction time, is an estimation of the time an individual needs to stop their usual behavior in response to the stop signal. Active THC, regardless of whether subjects were told or expected it, impaired inhibition on the Stop Signal Task.

Out of all the participants only a small proportion suspected that they were being deceived. Suspicions about the THC content were only reported by two participants (in the Told THC/Received Placebo condition) and by seven participants (in the Told Placebo/Received THC condition). In all cases, Both THC dose and marijuana expectancy independently increased subjective intoxication.

It is commonly known that real or perceived expectancies can play a part in influencing responses to other drugs, such as alcohol. Here, expectancy of smoking THC in combination with active THC increased perceptions of risk from risky alcohol use.

The effect of THC somewhat contributed to impaired inhibition — that is the pharmacological effect and not the perceived effect. Whereas expectancy of having smoked THC affected impulsive decision-making, with a compensatory direction of effect on some measures of risky decision-making. For example, independently from the THC administration, expectancy also increased perceived risk from coercive sex among women.

Researchers showed that THC can affect some mechanisms underlying impulsive behaviors while not affecting others. The study represents the first evaluation of independent and combined effects of smoking and expecting to smoke active marijuana on multiple measures of risk taking and impulsivity, using a balanced placebo design. It proved a way to independently tease out the expectancy that marijuana was smoked from the pharmacologic effect of delta-9-tetrahydrocannabinol (THC).

Originally appearing at All Results Journals

Image — source

ResearchBlogging.org

Metrik J, Kahler CW, Reynolds B, McGeary JE, Monti PM, Haney M, de Wit H, & Rohsenow DJ (2012). Balanced placebo design with marijuana: Pharmacological and expectancy effects on impulsivity and risk taking. Psychopharmacology PMID: 22588253

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2 Responses to “Ceci n’est pas la marijuana…”


  1. 1 thecellularscale June 25, 2012 at 04:58

    Really interesting. So basically if you think you are ‘messed up’ you might be more careful and take fewer risks to compensate?


  1. 1 URL Trackback on June 24, 2012 at 23:08
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