Smoking, Drinking and Cannabis in Your 20s: The Long Shadow on Memory

The S&P 500 is approaching 7,000. Oil fell 7%. Inflation came in far below forecast.

The quick scan: Tuesday delivered a second consecutive strong session, with the S&P 500 finishing at 6,967.38 – within touching distance of 7,000 and its highest level since before Operation Epic Fury began. Three things drove it: Iran reaching out to Washington hours after the blockade was announced, raising hopes of renewed negotiations; a dramatically soft inflation print (PPI came in at +0.5% vs +1.1% expected, with core PPI at just +0.1%); and big-tech megacaps resuming their role as market engine. Oil fell 7% to around $92 as the diplomatic signals filtered through.

S&P 500: +1.18% to 6,967.38 – knocking on the door of 7,000; the index has now recovered all its war-period losses and sits above its pre-war level
Dow Jones: +0.66% to 48,535.99 – gained 317.74 points despite a mixed bank earnings session; JPMorgan slipped 1% and Wells Fargo fell 2% despite beating expectations, while Citigroup posted its highest quarterly revenue in a decade
NASDAQ: +1.96% to 23,639.08 – the session's standout; Meta gained 4.3%, Amazon 3.96%, Nvidia 3.65% as the AI trade ran hard on the easing inflation outlook.

What's driving it: The diplomatic and economic signals aligned unusually well on Tuesday. Iran reportedly contacted Washington within hours of the blockade taking effect, with Pakistan now arranging a second round of US-Iran talks. UK Prime Minister Starmer and French President Macron are co-hosting a Paris summit Friday focused on reopening the Strait. On the data front, March PPI landed significantly below forecast at +0.5% against an expected +1.1%, with core PPI at just +0.1%. The soft read dramatically reduced stagflation fears and revived rate-cut expectations – the 10-year yield fell to 4.256%. Oil at $92 is still elevated but down sharply from its $113 peak. VIX fell to 18.36 – its lowest since before the war.

Bottom line: Two sessions in, the market has decided the blockade is a negotiating tactic, not an escalation. Whether that read is correct will become clearer at the Paris summit Friday and in any follow-up Islamabad talks. The PPI data is genuinely encouraging – if March CPI follows the same pattern, the Fed's path to rate cuts re-opens. For L-Plate Retirees, the S&P at 6,967 is a useful reminder that the ten days between the blockade announcement and today have produced not panic, but a rally to pre-war highs. Which is why having a plan matters more than having a reaction.

Your 20s Called. They Want to Talk About Your Brain.

The scoop: Here's an uncomfortable question to sit with on a Wednesday morning: what you were doing at 22 may still be showing up in your brain at 55.

New research from the University of Michigan, published in the Journal of Aging and Health, followed 16,000 Americans from age 18 all the way into their 50s and 60s, tracking three habits that researchers call the "triple threat" of substance-related cognitive risk: daily smoking, binge drinking and frequent cannabis use.

The study's lead researcher, Dr Megan Patrick, principal investigator of the Monitoring the Future Longitudinal Panel Study, was direct: "Substance use has both acute and long-term effects on health and well-being. Poor memory is a common sign of early dementia. Identifying the risk factors that can lead to dementia is crucial for the prevention and treatment of cognitive decline."

The findings are sobering – but more nuanced than the headline suggests. Because the three substances don't damage memory the same way at all.

How the study worked.

Every few years from ages 18 to 30, participants reported how often they drank, smoked or used cannabis. Researchers counted the number of "waves" of heavy use – defined as daily smoking, binge drinking (five or more drinks in a row in the past two weeks), or cannabis use 20 or more days a month.

By midlife, they asked participants a single question: "Would you say your memory is excellent, very good, good, fair, or poor?" Anyone answering "fair" or "poor" was considered to have poor self-rated memory. About one in ten participants fell into that category by their 50s and 60s.

This was not a clinical cognitive test. The researchers were clear that self-rated memory is a validated early indicator of cognitive decline – not a diagnosis. But poor self-rated memory in midlife is a meaningful signal; previous studies have linked it to later dementia risk.

The surprise: three substances, three very different stories.

Cigarettes: the damage is direct, and quitting doesn't undo it.

This is the most confronting finding for anyone who smoked in their youth. Each additional wave of daily smoking in young adulthood raised the odds of poor memory decades later by around five percent. More importantly, this held even after accounting for whether people were still smoking at 35.

Quitting by midlife did not erase the risk.

The cumulative exposure in young adulthood itself appears to cause lasting harm, likely through the gradual narrowing of blood vessels that supply the brain and the inflammatory effects of chronic nicotine exposure during the brain's most sensitive developmental window.

The human brain continues developing into the mid-20s, particularly in the regions responsible for impulse control and decision-making. Substances absorbed during this window of heightened neuroplasticity have an outsized capacity to rewire neural pathways.

Alcohol: the key is whether it became a disorder.

The alcohol findings are more nuanced, and in some ways more hopeful.

Each wave of heavy drinking in young adulthood raised the odds of poor memory by 13% – a meaningful number that persisted 30 to 40 years later. But when researchers accounted for whether someone had developed alcohol use disorder by age 35, that direct link largely disappeared.

The interpretation: for people who drank heavily in their 20s but stopped before midlife and never developed a clinical disorder, the long-term memory risk appears to be limited.

The risk concentrates in those whose heavy drinking continued into a disorder. People with alcohol use disorder at 35 were 32% more likely to report poor memory in late midlife compared to those who drank without developing a disorder.

In the study sample, more than a quarter of participants showed signs of alcohol use disorder by age 35 – a figure that puts a very large group in the higher-risk category.

Cannabis: same pattern as alcohol – it's the disorder that damages, not the use itself.

Cannabis follows a similar pathway to alcohol. Frequent use in young adulthood was associated with an 8% increase in poor memory risk per wave – but this association largely disappeared once the researchers accounted for cannabis use disorder by midlife.

Those who used cannabis heavily in their 20s but did not develop a use disorder showed no lasting memory impact. But those who developed cannabis use disorder – defined as marijuana use causing significant life problems or loss of control – were 36% more likely to report poor memory later in life.

The critical path: heavy cannabis use in the 20s raised the odds of developing cannabis use disorder by age 35, which in turn damaged memory. Young adult use was a risk factor for the disorder, which was the actual mechanism of harm.

The takeaway in plain terms.

Three substances. Three mechanisms. One common thread.

Smoking damages memory cumulatively and directly – the earlier and heavier the exposure, the more lasting the harm, and quitting later doesn't fully reverse it.

Alcohol and cannabis damage memory primarily through the pathway of disorder. Use that didn't become problematic, and that didn't persist into midlife as a clinical condition, appears to carry limited long-term memory risk.

This matters because it reframes the question. It's not simply "did you drink or use cannabis in your 20s?" It's "did that use develop into something that controlled you?"

Actionable takeaways for L-Plate Retirees:

• If you smoked in your 20s, the memory risk is real – even if you quit. This is not meant to be demoralising, but it is worth taking seriously. The cumulative brain exposure from young adult smoking is not fully reversible. This makes maintaining other protective brain health habits – exercise, social connection, sleep, diet – all the more important as a counterbalance.

• Heavy drinking that didn't become a disorder may carry less lasting risk than feared. Many people look back at their 20s with anxiety about how much they drank. If that drinking never crossed into clinical disorder and you moderated by midlife, the Michigan study suggests limited long-term memory impact. This is not a green light to drink heavily now – it's a distinction about what happened then.

• The disorder threshold is the real risk marker. For both alcohol and cannabis, the research points to substance use disorder – not use itself – as the primary mechanism of memory harm. If past use never reached the level of causing life problems or loss of control, the direct cognitive risk was likely lower than commonly assumed.

• Current heavy use is a different conversation. This study was specifically about young adult use and its long-term legacy. Heavy, frequent substance use in your 50s and 60s carries its own direct risks to brain health that are separate from this research.

• This is further evidence for quitting smoking now. Even though the study found that quitting by 35 didn't fully undo past damage, every year without smoking allows blood vessels to partially recover and reduces ongoing vascular damage to the brain. The earlier you stop, the better – but stopping at 60 still matters.

• Brain health is a long game that started decades ago. The Michigan study covers ground that most of us can't redo. What we can do is make sure the habits we have now – sleep, exercise, alcohol moderation, social engagement – are working to protect cognitive function, not erode it further.

Your Turn:
Looking back at your 20s, which of the three – smoking, drinking, or cannabis – do you think you'd describe as genuinely problematic at the time, and how did that change as you got older?
The study draws a meaningful distinction between heavy use and use disorder. Does that framing change how you think about your own history, or that of people you know?
The brain is most vulnerable to substances during its developmental window in the 20s. Are there conversations you'd want to have with younger people in your life – children, grandchildren – based on what you know now?

👉 Hit reply and share your thoughts – your answers could inspire fellow readers in future issues.

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