Bottom line
Nicotine in tobacco and THC in cannabis are both addictive substances that act on the brain. The bills differ. Both come due 3.
The smoking bill is the clearest. The British Million Women Study estimates that people who keep smoking live at least ten years less on average. Quitting before 40 avoids more than 90 percent of the excess deaths. Quitting before 30 avoids 97 percent 5.
Nicotine itself can sharpen focus and cognition for a short time. Those gains are overwhelmed by dozens of carcinogens in tobacco products and by the cardiovascular harm 3.
The cannabis bill is younger and blurrier. A meta-analysis found that people who have ever used cannabis have about a 40 percent higher risk of psychosis, and the most frequent users about double. A 2025 meta-analysis linked cannabis use to higher risk of heart attack, stroke, and cardiovascular death. Cause is still not settled 67.
On sleep, THC makes people fall asleep faster, then suppresses REM sleep the way alcohol does. With long use, tolerance sets in and stopping rebounds. CBD has less data, and the direction is milder 1.
What it is
Nicotine is an alkaloid in the tobacco plant. It is the addictive component that produces the "hit" and makes tobacco products hard to put down. Smoke, vapor, and the leaf also carry dozens of carcinogens 3.
Cannabis, often called marijuana, has two core components. THC is the psychoactive piece that produces the high. CBD does not intoxicate, and it acts more on mood and anxiety 3.
THC's site of action is the brain's cannabinoid receptor, CB1. The body makes similar molecules of its own, including anandamide, a "bliss molecule" that helps regulate stress, appetite, and mood. Incoming THC occupies that system by force 4.
Tolerance and dependence are shared features of the system. After repeated use, the same amount feels weaker, and more is needed to get back to the starting point. Stopping brings withdrawal discomfort 34.
E-cigarettes and vaporizers avoid tar and other products of burning. Long-term effects are still unknown 3.
Medical and recreational cannabis differ. Medical products usually have a set CBD-to-THC ratio. The U.S. regulator has not recognized cannabis as a treatment for any disease, but it has approved individual cannabis-derived drugs, such as the cannabidiol preparation Epidiolex 2.
Why it matters
A British study of about a million women is the largest set of numbers. People who keep smoking live at least ten years less than never-smokers, and about two thirds of deaths among women smokers from their fifties through their seventies were caused by smoking 5. Quit before 40 and excess deaths are a tenth of those in people who keep smoking. Quit before 30 and less than 3 percent remains 5.
A meta-analysis of 24 studies found worse performance in chronic smokers on cognitive impulsivity, attention, short- and long-term memory, and cognitive flexibility. Cross-sectional, consistent direction, cause hard to pin down 8.
The cannabis bill concentrates on mental health. A 2007 systematic review in *The Lancet* pooled multiple prospective studies. Psychosis risk was about 40 percent higher in any user and about double in the most frequent users. The authors judged that the risk still stood after confounding and the short-lived intoxication were set aside 6.
Cardiovascular disease is a newer line on the bill. A 2025 meta-analysis in *Heart* estimated that cannabis use was associated with about a 30 percent higher risk of acute coronary syndrome, about 20 percent higher stroke, and about a doubling of cardiovascular death. The authors also call for actively asking about cannabis use in patients with serious cardiovascular disease 7.
In an interview, Walker says THC is not a good sleep aid for adolescents, because their brains are still developing 1.
Cannabinoid hyperemesis syndrome, after long heavy use, is repeated vomiting that a hot shower can ease for a while. Hill discussed it in an interview 4.
Different perspectives
Main positions
Accounts that deal with cannabis directly come mainly from medical commentary and from the sleep series 21.
In 2023 that commentary addressed cardiovascular risk from medical cannabis. The basis was a Danish cohort reported at a European Society of Cardiology meeting: cardiovascular-event risk may be higher in medical-cannabis users. The stance is that it is worth watching, and that one study is not a conclusion. Studies of this kind have trouble separating the pain itself, other drugs taken at the same time, and the cannabis 2.
The same commentary clears up the regulatory picture. Medical products have a more controllable ratio. What the U.S. regulator has approved is individual purified drugs, not "cannabis" itself, and prescribing practice in Denmark and elsewhere differs from the United States. Treating "medical" as "harmless" is a different claim 2.
In the sleep series, Walker was asked directly in an interview about THC and CBD for sleep. His words were "No. I don't think I'd feel comfortable in suggesting that it's a pro sleep compound." He is unwilling to call THC a sleep-promoting substance 1.
His reasons are specific. THC does shorten the time to fall asleep, but like alcohol it suppresses REM sleep. With regular use, even the faster-sleep benefit disappears. After stopping, many people hit rebound insomnia. CBD has less data and looks more hopeful. Early evidence shows it does not suppress REM, dependence looks smaller, and there may be a U-shaped range where it works better. Differences between strains, sativa and indica, lack data 1.
One site files this theme under alcohol, tobacco, and cannabis. The opening tone is no shaming and no judgment. The choice is personal. Knowing the consequences lets a person decide with more information 3.
On tobacco, the topic page is direct. Nicotine raises cognition and focus in the short term, and that small gain is far outweighed by the long-term risks of tobacco use: higher blood pressure, less blood flow to organs and brain, and cancer, stroke, heart attack, and cognitive decline from dozens of carcinogens 3.
On quitting, the page offers a toolbox. Patches, gum, and nasal spray can manage withdrawal and step the amount down. Clinical hypnosis has shown some promise. There are medication paths as well. All of that is discussed with a clinician 3.
On cannabis, Matthew Hill of the University of Calgary was invited to talk it through — and the occasion was that Hill had publicly criticized earlier statements on cannabis, psychosis, and strain differences 4.
The main points of that conversation: THC and CBD have different pharmacology. Legality is not safety. After legalization in Canada, the largest rise in use was in people 55 and older, especially women. Psychosis risk deserves more worry in people with a particular genetic background. A cardiovascular signal exists, but the data are not as clean as cigarettes and lung cancer 4.
Hill's words on the heart, in that conversation: there is "something" between cannabis and stroke or cardiac events, but the relationship is still nowhere near as clear as cigarettes and lung cancer once were 4.
Shorter public clips cover the same ground from another angle. One explains why THC and alcohol are not reliable sleep aids. They help falling asleep at first, then disrupt sleep structure, and stopping THC brings a rebound of insomnia 9. Another covers how common substances concentrate in breast milk — caffeine, cannabis, alcohol, and nicotine are all on the list — so someone who is nursing has an extra weighing to do 10.
Where views agree and differ
Three points of agreement:
- The long-term harm of tobacco products far exceeds nicotine's short-term cognitive gain. Quitting is never too late, and earlier is better 35.
- Cannabis is not harmless, especially in young people, people with a family history of psychosis, and people with cardiovascular disease. Those risks need their own weighing 647.
- Medical use and recreational use are different things. Legal and safe are different things too 24.
Three points of tension:
- How psychosis risk is told. An earlier account stressed that cannabis might trigger psychosis in some people, and Hill criticized that in public as overstated. Hill's version stresses genetic susceptibility and the roles of amount and frequency. After the conversation both agreed the data exist and the interpretation has room 4.
- How certain the cardiovascular risk is. One topic page lists it as one chronic risk. Hill thinks a signal exists and is not yet clean. The medical commentary gave the Danish study only "watch it, it is not proven." These accounts stop at association, pending more evidence 342.
- Cannabis as a sleep aid. Walker's "no" is the bluntest. One topic page includes timestamps on THC suppressing REM and on withdrawal affecting sleep 13.
PearHealth's synthesis
What we take: the lifespan bill for smoking rests on million-scale prospective cohorts, and the benefit of quitting is equally clear 5.
What we hold back: cannabis bills for psychosis and the heart are observational. Confounding — who uses it, why, and what else — cannot be fully removed. A higher average risk is not a personal certainty. For higher-risk groups the cautious direction agrees 67.
Three cautions. Adolescents using THC for sleep: Walker says the developing brain is still growing, and THC is not a good sleep choice for them. That call belongs with a clinician 1. Cannabis for sleep works short term, then tolerance and rebound on stopping 1. Quitting smoking is worth doing with a clinician. The tools go beyond willpower 3.
We do not sell nicotine replacements, cannabis products, or related supplements.
How strong is the evidence
"Smoking shortens life, and quitting saves it" is the firmest evidence here. A prospective cohort of a million women, decades of follow-up, an effect too large for confounding to explain. It is still observational, and it agrees across countries closely enough to be near settled 5.
"Chronic smoking is associated with cognitive impairment" is a cross-sectional meta-analysis. The direction agrees. Both stories are still alive: smoking came first and performance worsened, or people who were already impulsive became smokers 8.
"Cannabis and psychosis risk" is a systematic review of prospective studies. The authors specifically handled confounding and reverse causation and still judged the risk to stand. Absolute risk is small and individual differences are large. A group number does not assign a personal fate 6.
"Cannabis and cardiovascular events" is a 2025 meta-analysis. The authors themselves flag heterogeneity and the limits of real-world data 7.
"THC disrupts sleep structure, and CBD is unproven" comes from literature review and expert judgment. Large randomized trials are missing. Walker also says plainly that CBD research has trouble even getting funded 1.
Inhaled routes make the harm path easier to see, and oral routes have an amount that is hard to control. That is an inference from mechanism and emergency data, with no head-to-head long trial 34.
What you can do
One workable direction: people who do not smoke do not start because of claims that nicotine sharpens focus. People who smoke treat "when to quit" as a concrete question for a clinician. People who use cannabis know what their amount, frequency, and family history imply.
Directions many people take:
- Smokers set a quit date and, with a clinician, talk through nicotine replacement (patches, gum, and the like) together with medication paths 3.
- Strong discomfort in withdrawal is not something to white-knuckle. A management plan is discussed with a clinician, and common relapse triggers are listed ahead of time 3.
- People using cannabis for sleep write down, for a few days, faster sleep onset next to a lighter second half of the night, fewer dreams, and how the next day feels 1.
- Whether to use THC in adolescence, pregnancy, or while trying to conceive is a clinician's judgment. The special vulnerability of the developing brain is stated in these discussions 1.
- People with heart disease, a history of stroke, or a family history of psychosis tell a clinician that history before using 67.
- People who need cannabis for pain, nausea, or another medical purpose use a formal medical path, rather than treating a recreational product as a drug on their own 2.
- Watch older adults at home. People 55 and older are among the fastest-growing groups of cannabis users, and their cardiovascular risk is more worth weighing 4.
Questions worth raising with a clinician:
- I have tried to quit several times and not managed it. Is a medication path a fit 3?
- I use cannabis for sleep. How do I tell when it has started to work against my sleep 1?
- I have angina or a family history of stroke. What does cannabis mean for me 7?
- My child is encountering cannabis in adolescence. What does a parent need to know 16?
Common misconceptions
Misconception one: an e-cigarette is harmless water vapor. It avoids combustion products, nicotine itself is addictive, and the topic page says long-term effects are unknown, with possible health risks 3.
Misconception two: nicotine sharpens focus, so smoking helps the brain. That short gain is outweighed by carcinogens and reduced blood flow. Chronic smokers do worse on several cognitive tests 38.
Misconception three: cannabis is a natural plant, milder than alcohol. Natural and safe differ. Links to psychosis and to the heart are accumulating. Legal is not harmless 674.
Misconception four: cannabis helps sleep and beats sleeping pills. THC shortens time to fall asleep and suppresses REM. Tolerance removes the benefit, and stopping brings rebound insomnia. Walker will not call it sleep-promoting 1.
Misconception five: indica relaxes, sativa excites, and strain science is mature. Walker says the data do not separate strains on sleep. Hill has criticized that popular account too 14.
How it connects to your blood work
No blood test directly reads "how much nicotine or cannabis has harmed." Both substances touch several systems, and the markers below are worth reading with use in view.
- Carboxyhemoglobin is not on the routine list. If a red-cell count (rbc-count) or hematocrit (hematocrit) was drawn, tell the ordering clinician about smoking.
- Total white cells (wbc-total) and high-sensitivity C-reactive protein (hs-crp): smoking is tied to chronic inflammation, so inflammation readings are interpreted with smoking status.
- HbA1c (hba1c) and fasting markers: weight gain after quitting is a common pattern. The long path of metabolic markers is worth reading alongside the quit plan.
- Testosterone and other hormone markers: in an interview, Hill talks about links between cannabis and hormones, breast tissue growth in men, and sperm quality. Related hormone checks are worth reading with cannabis use disclosed 4.