By Tom Horvath, PhD
We know how to estimate levels of alcohol moderation and intoxication. For instance, we can estimate that a 180 pound male, without a history of alcohol dependence, drinking over two hours, might hardly feel one drink, would be mildly buzzed at two or three drinks, would be substantially buzzed (and over the legal driving limit) at 4 to 6 drinks, and intoxicated to heavily intoxicated at 10 drinks. Almost anyone can make these estimates because blood alcohol level (BAL) calculators are widely available. They are based on a “standard drink,” the differences between how men and women on average metabolize alcohol, time drinking, and body weight. We can interpret the BAL because we understand the average expectable behavior at different BAL’s. In the example above, 10 drinks correspond to a BAL of .21, and that BAL indicates intoxication.
This knowledge has led to recommendations about what moderate drinking consists of. One of the most widely recommended moderation guidelines is, for men, 2 standard drinks per day or a max of 14 per week (with drinking spread over several days), and for women, 1 standard drink per day or a max of 7 per week (with drinking spread over several days). These moderation guidelines are not suggesting that this level of alcohol use is safe, only that the risk/reward ratio at this level of consumption is relatively favorable and would get more unfavorable with higher consumption.
Cannabis (marijuana, weed, pot) has been a challenge because we do not have comparable knowledge of how to measure blood cannabis levels, or how to interpret those levels in terms of average expectable behavior or potential damage to the user. However, recent work has made progress on this challenge.
Psychological scientists at the University of Bath in the United Kingdom examined the incidence of cannabis use disorder at various levels of THC use (the active ingredient). Using 40 mg of THC as the unit (or 1/3 gram of herbal cannabis), they found that individuals using more than 8 units per week were at much higher risk for cannabis use disorder (CUD).
In one sample, 80% of those below 8 units did not have CUD, and 70% of those above that threshold did.
We now have what may be our first evidence-informed estimate of moderate cannabis use: 320mg of cannabis per week or less. Ideally, the cannabis products we purchase will have labels clear enough to allow this calculation. Future legislation might require improved labeling. As with alcohol moderation, 320 mg of THC use per week is not “safe,” but the risk/reward ratio is relatively favorable for those who wish to use cannabis.
