A Reddit thread asked recently: why does nobody talk honestly about what cannabis actually does to you, all of it, not just the good parts? The cannabis industry has an obvious incentive to emphasize benefits. The anti-cannabis side has an equal and opposite incentive to emphasize harms. Neither produces a complete or accurate picture. Here is an honest, complete inventory of cannabis side effects, distinguishing short-term from long-term, THC from CBD, occasional from heavy use, and documented from claimed.
Quick Answer: What Are the Side Effects of Cannabis?
Short-term THC side effects include dry mouth, red eyes, increased heart rate, impaired short-term memory, slowed reaction time, anxiety at higher doses, and impaired coordination. Long-term heavy use is associated with cannabis use disorder in approximately 9 percent of users, respiratory effects from smoking, possible cognitive effects that are largely reversible with abstinence in adults, and increased psychiatric risk in predisposed individuals. CBD has a much more limited side effect profile primarily including fatigue, diarrhea at high doses, and drug interactions.
Short-Term Side Effects of THC
Dry Mouth (Cottonmouth)
One of the most universal and predictable cannabis side effects. THC activates CB1 receptors in the salivary glands, suppressing saliva production. Almost every cannabis user experiences this. Staying hydrated reduces discomfort. Not medically significant but uncomfortable.
Red Eyes
THC lowers blood pressure and dilates blood vessels, including those in the eyes. This causes the characteristic redness. Not harmful. Can be reduced with over-the-counter eye drops designed for redness. Less pronounced in experienced users with tolerance.
Increased Heart Rate
THC can increase heart rate by 20 to 50 beats per minute in the hour following consumption. For most healthy adults, this is not dangerous. For people with heart conditions, this cardiovascular effect warrants careful consideration and physician consultation before using cannabis.
Impaired Short-Term Memory
THC impairs the hippocampus’s ability to form new short-term memories during intoxication. This is a well-documented, reproducible effect. It reverses when THC clears. This is why cannabis users sometimes lose track of what they were saying or doing during a session.
Slowed Reaction Time
Cannabis impairs reaction time and psychomotor performance. This is relevant for driving and any activity requiring quick reflexes. The impairment is real even when the user subjectively feels capable.
Anxiety and Paranoia
At moderate to high doses, THC activates the amygdala in ways that produce anxiety and paranoia in some users. This is the single most common negative side effect and is strongly dose-dependent. High-THC products produce this effect more reliably than low-THC or balanced CBD-to-THC products.
Impaired Coordination
THC affects the cerebellum and basal ganglia, which coordinate movement. This produces the impaired balance and coordination associated with cannabis intoxication and is the primary reason cannabis impairs driving.
Appetite Stimulation
The munchies are real. THC activates hypothalamic circuits that stimulate appetite. This is a side effect for recreational users trying to manage their diet and a therapeutic benefit for cancer patients and others with appetite loss.
Side Effects Specific to Delivery Method
Smoking and Combustion
Smoking any plant material produces combustion byproducts including carbon monoxide, tar, and carcinogens. Chronic heavy cannabis smoking is associated with chronic bronchitis and increased respiratory symptoms. Unlike tobacco, cannabis smoking has not been clearly linked to lung cancer in epidemiological studies, possibly because cannabis users smoke significantly fewer cigarettes-worth of material than tobacco smokers. Vaporizing eliminates combustion byproducts.
Edibles and Overconsumption
The delayed onset of edibles creates a specific side effect profile: easy to overconsume, producing an intense, prolonged, anxiety-inducing experience that can last 6 to 12 hours. The most common cause of cannabis-related emergency room visits, particularly among first-time users and tourists in legal states.
Concentrates and Dabs
High-potency concentrates can produce effects significantly more intense than flower at equivalent doses. Novice users and people returning after a tolerance break can be severely affected by concentrate doses that experienced users tolerate comfortably.
Long-Term Side Effects of Regular Use
Cannabis Use Disorder
Approximately 9 percent of people who use cannabis develop cannabis use disorder at some point, rising to 17 percent among daily users. Cannabis use disorder involves continued use despite negative consequences, difficulty reducing use despite wanting to, and withdrawal symptoms when stopping. Cannabis withdrawal produces real symptoms including irritability, sleep disruption, anxiety, and appetite changes that typically resolve within two weeks.
Cognitive Effects
Heavy adolescent cannabis use is associated with cognitive effects including reduced verbal memory and processing speed that may persist into adulthood. In adults who begin use after brain development is complete (mid-to-late 20s), cognitive effects from regular cannabis use appear largely reversible with extended abstinence of one month or more. The evidence for lasting cognitive harm in adult-onset users is significantly weaker than for adolescent-onset users.
Psychiatric Risk
Cannabis use, particularly high-THC use, is associated with increased risk of psychosis in genetically predisposed individuals. People with a personal or family history of schizophrenia or other psychotic disorders face a meaningfully elevated risk from regular cannabis use. This is a genuine clinical concern, not a prohibitionist talking point, though the absolute risk in people without a predisposition is much lower.
Respiratory Effects From Chronic Smoking
Chronic heavy cannabis smoking is associated with increased phlegm production, chronic cough, and bronchitis symptoms. These effects are reduced or eliminated by switching to vaporization, edibles, or other non-combustion delivery methods.
Side Effects of CBD
CBD has a significantly more limited side effect profile than THC. The most commonly reported side effects from CBD at therapeutic doses include fatigue and sedation at higher doses, diarrhea at high doses particularly above 300mg, nausea in some individuals, and dry mouth similar to but less pronounced than THC-induced cottonmouth.
CBD’s most significant clinical concern is drug interactions. CBD inhibits liver enzymes including CYP2C9 and CYP3A4 that metabolize many common medications including blood thinners, antiepileptics, and some antidepressants. This is a real clinical concern for anyone on prescription medications.
Frequently Asked Questions
Can cannabis kill you?
No documented deaths are attributable to cannabis toxicity alone in adults. The estimated lethal dose based on animal studies is far beyond what a human could realistically consume. Cannabis is not without health risks but acute fatal toxicity is not one of them.
Does cannabis cause lung cancer?
Unlike tobacco, cannabis smoking has not been clearly linked to lung cancer in epidemiological research. Combustion byproducts are present and chronic heavy smoking is associated with respiratory symptoms. The lower frequency of cannabis smoking compared to tobacco smoking is thought to reduce the carcinogenic exposure sufficiently to explain the difference in cancer risk.
Is cannabis addictive?
Cannabis produces psychological dependence in some users. Cannabis use disorder affects approximately 9 percent of users overall and 17 percent of daily users. The withdrawal syndrome is real but not medically dangerous unlike alcohol withdrawal. Cannabis is less addictive than alcohol, tobacco, opioids, or cocaine by any standard measure.
Author: Sarah Kim covers cannabis science and wellness for Ganjly.
Related: Read Ganjly’s guide to cannabis vs alcohol research and cannabis tolerance breaks.
