Those who use heavily in Adolescence can lose something like 6 or 8 IQ points, among other negative effects. Those who start as adults and stop don't seem to have the same effects[1], but it is unclear how much that reflects lower baseline IQ of users vs. the impact of marijuana itself.
I would like some perspective on what a 6-8 IQ point difference actually means in real life.
I know IQ is on a curve so if I'm on the lower end and dope up I might not qualify for the military against had I not doped up by such a margin window.
For an average person, what can the person sitting next to me do +8 IQ that I can't? What can the person sitting in front of me not do at -8 IQ that I can?
Granted I've encountered "slow" and "fast" people in my life, but I have little idea how to relate that to an IQ number besides "higher" and "lower" like a water faucet for temperature.
If we think in terms of a race -- an IQ of 100 puts you at the 50th percentile -- so half of the contestants are faster than you, and the other half are slower.
A loss of 6-8 points puts you at about at about the 35th percentile -- meaning 65 percent of the people in the race will be running more faster than you. Or (back in real life terms) be that much more likely to get admitted to college, get a decent job / spouse, and so on.
That is, to the extent that definitions of IQ are valid and can be measured accurately, and so on. But given the amount of research that has gone into this -- and we know a lot more now that we did a few decades ago -- it seems the risks (of heavy cannabis use) are potentially quite serious.
(BTW, as to how one gets from "6-8 points" to "35th or 40th percentile": it has to do with how the IQ scale is defined. By the traditional scale approximately two-thirds of the population scores are between IQ 85 and IQ 115. Meaning (on a scale from 1 to 100) 15 points of IQ equals a difference of about 33 percent. So 6-8 points is about half that, or very roughly 15 percent).
100 is defined as an "average" IQ, yet I suspect everyone on this site is quite a bit above that, likely in the 110-120 range and skewed heavily upwards, and have not actually interacted constantly on a long term with someone who has a ~100 IQ, much less a ~92 IQ.
It's actually somewhat amazing how isolated you can get from the average person if you stick to settings & persuits associated with "intellectuals". I recall ended up in a friend group of 8 people once that included 3 geniuses.
Sometimes you really have to take a step back and realise that you're not as normal as you feel. You can spend your time on hackernews feeling very insecure and then apply 5% of what people talk about here and then the average person will treat you like you invented fire.
Fun fact: Ivy League students who attended public high schools hold sharply lower opinions of what "average people" are able to do than do students who attended private high schools.
To this end: I’ve astonished a number of peers who did the straight to a 4-year track with a anecdote about only 22% of my community college “Critical Thinking” class passing the first midterm, which covered very simple truth functions and negation. To this day it sticks with me.
Remember the 100 includes those with mental disabilities or borderline disabled. If you are in a building without people with mental disabilities then the IQ is likely some amount above 100.
So when you think of your highschool class you shouldn't think 100, but rather 105. So even though 100 is the average of the population it can be on the lower end in a professional or academic setting.
Based on my own reading of IQ and general heuristics I've developed from observing people (i.e. this is my folk wisdom, I am not sharing links), on a team of SDEs, the one SDE who is really really sharp, not just due to tenure, but generally just grasps things faster and earns the intellectual respect of his peers, is probably about 8-15 points higher than the average IQ of the SDEs around. Again, this is super heuristic, as IQ is non-linear.
A population average loss doesn't even mean that I'll deterministically lose 6 to 8 IQ points. But it's strong enough evidence that it severely fucks with the brain for me to stay the hell away. The direct effect of the loss of a few IQ points is not the issue.
The theory is that heavy use during adolescence leaves permanent changes in adulthood. Heavy usage that starts in adulthood doesnt' seem to have the same level of permanent effects.
If you smoke heavily and quit, your endocannabinoid system underperforms by about 20% for two or three weeks. It basically dulls pleasure in everything, producing anhedonia, depressed appetite and irritability. It impacts sleep negatively too.
Each time I've quit for an extended period of time it's taken me about three weeks to feel normal. During those weeks I definitely feel more grumpy and irritable. I'm also curious as to whether THC or other chemicals in the smoke have any effect on the body's thermoregulation, because each time I've quit I've also woken up drenched in sweat every night for about the first week or so. Crazy dreams as well.
These have all been me going cold turkey after heavy daily use for extended periods of time.
It does. My understanding is that THC inhibits REM sleep, and as a result the chemicals that are usually released during the REM phase that cause you to dream do not get released. Once you quit and start having REM sleep again, there's a "backlog" so to speak of the chemicals and more than usual are released, thus causing the extremely vivid dreams.
[1] https://www.drugabuse.gov/publications/research-reports/mari...