Understanding why cannabis doesn't affect everyone the same way is key to making informed decisions. The answer lies in a mix of biological, psychological, and social factors, in addition to the chemical composition of the plant and the form of consumption (smoking, vaping, or ingesting).
In this article we gather and reformulate the available scientific and technical evidence on the effects of cannabis, its short- and long-term risks, and its impact on the mental health, cognitive performance, and safetyAnd why the age of onset, the dose, and the context make such a difference.
Why does cannabis affect each person differently?
Cannabis contains over 400 compounds, including dozens of cannabinoids. The main compound responsible for the "high" is THC (delta-9-tetrahydrocannabinol), whose potency varies between plants and extracts, with selected varieties reaching very high percentages. Other compounds also act alongside it, such as CBD often mitigates some of the adverse effects of THCCBN, THCV, and terpenes, which can modulate the experience: for example, the CBD often mitigates some of the adverse effects of THC, including anxiety, and can affect your metabolism.
These compounds interact with the human endocannabinoid system, which includes CB1 receptors (abundant in the brain: cortex, hippocampus, cerebellum, basal ganglia, insula, cingulate gyrus, nucleus accumbens) and CB2 receptors (more prevalent in immune system cells). Activation of CB1 receptors alters the release of neurotransmitters such as dopamine, norepinephrine, glutamate, and GABA, explaining changes in mood, perception, memory, motivation, and coordination.
The route of administration greatly influences the onset and intensity: smoking or vaping produces peak plasma levels within 15-30 minutes; ingestion delays the onset (30-120 minutes) but prolongs the effect because some THC is converted into 11-hydroxy-THC, an equally active metabolite. Due to its lipophilic nature, THC accumulates in body fat, is released slowly, and can be detected in tests for days or weeks in regular users. This pharmacokinetics explains why tolerance develops after several days or weeks of repeated use.
In addition to phytocannabinoids, the body produces endocannabinoids (such as anandamide), which are involved in basic functions like feeding and reward. The endocannabinoid system participates in such primal behaviors as lactation in mammals, illustrating its importance. evolutionary and physiological relevance beyond recreational use.
Acute (short-term) effects: what you notice and how long they last
After consumption, many people describe a feeling of well-being, relaxation, or euphoria, along with an altered sense of time and distance. Psychomotor slowing, impaired hand-eye coordination, increased appetite, red eyes, and dry mouth are not uncommon. At moderate to high doses, especially in inexperienced individuals or in unfamiliar environments, the following may occur: anxiety, panic, paranoia, or confusion.
In cardiovascular terms, the most immediate effect is an increase in heart rate (20-50% above baseline; other data extend the range to 100% depending on the dose and individual). Fluctuations in blood pressure with postural dependence are also described: it may rise when sitting and fall when standing, favoring the orthostatic hypotension and dizziness at onset.
Acute cognitive impairment includes reduced sustained attention, worse working memory, and increased response latency, resulting in difficulties performing tasks requiring accuracy or speed. In driving, doses of 300 µg/kg of THC have been equated to blood alcohol levels exceeding 0,05 g/dl; even those who "compensate" by driving more slowly show clear deterioration in lane following and reactions.
Onset of action: If smoked or inhaled, the peak occurs within minutes and typically lasts 2-4 hours. With edibles, the onset is slower and the effect lasts 4-10 hours (or longer, if the dose is high), which explains some episodes of excessive consumption: the person repeats doses because they "don't feel anything" at the beginning and hours later. intense effects appear.
- Frequent short-term effects: feeling of calm or euphoria, slowed reaction and coordination, dizziness, time distortion, difficulty concentrating, remembering and reasoning, red eyes, dry mouth and increased appetite.
- Possible adverse effects: intense anxiety or panic, paranoia, hallucinations at high doses, increased pulse and, in some, increased blood pressure.
- Safety: Starting at ~10 mg of THC, an occasional user may experience impaired perception and psychomotor skills, impacting risky activities such as drive or operate machinery.
Chronic (long-term) effects: what may remain
Continued use has been linked to difficulties with attention, memory, and learning, as well as impairments in processing complex information. Studies with chronic users show changes in brain activity patterns (e.g., increased frontal alpha activity, decreased baseline cerebellar activity) and deficits in working memory. verbal fluency and processing speed.
People with persistent substance use may report apathy or decreased initiative (commonly known as "amotivational syndrome"), impacting academic or work performance. This includes abandoning hobbies, a reduced ability to set goals, and poorer adherence to routines, which in the medium term translates into worse quality of life and weakened social ties.
In mental health, chronic use has been linked to anxiety and depressive symptoms, with some nuances: some people use it to alleviate discomfort, but in the long run it can worsen symptoms or mask underlying problems. In vulnerable individuals, it has been described as triggering or exacerbating episodes. psychotic and mood disorders.
Dependence exists and is well-documented. Cannabis affects the brain's reward circuits through dopamine, and a proportion of users develop cannabis use disorder (DSM-5). It is estimated that between 7-10% of those who try it become addicted, a percentage that rises to around 17% if use begins in adolescence, and that approximately 1 in 3 users regular may present dependenceWithdrawal syndrome includes irritability, anxiety, disturbed sleep, and decreased appetite, with maximum intensity in the first few days.
Adolescence: a particularly sensitive window
The adolescent brain is undergoing rapid development, particularly frontal, limbic, and hippocampal circuits related to memory, motivation, and decision-making. Several studies show that cannabis can alter neuronal synchrony in the hippocampus, affecting immediate memory. Therefore, frequent use during this stage is associated with a higher likelihood of cognitive decline and mental health problems long term.
It has also been observed that starting earlier increases risks: a greater likelihood of dependence, poorer academic performance, and greater exposure to incidents (e.g., traffic accidents). Adolescents predisposed to psychosis show a marked increase in the risk of psychotic symptoms with use; risk increases of 25% to 51% have been reported in predisposed individuals, compared to more modest increases (15% to 21%) in those not predisposed. They have that vulnerability.
Mental health: anxiety, depression, and psychosis
Anxiety is one of the most common acute adverse effects, with panic attacks reported in a significant percentage of recreational users (20-30% in some studies). CBD may mitigate some of this reaction, but the response depends on the dose, the type of product, and the individual sensitivity.
In depression, the associations are complex: some users seek relief, but chronic use can be linked to more persistent depressive symptoms and, in some cases, to anhedonia (difficulty experiencing pleasure), especially in young people. Regarding psychosis, transient symptoms have been described after heavy use, which usually subside within 6 hours, although at high doses and in vulnerable individuals they can last for days; in the long term, use can precipitate or aggravate psychotic disorders following dose-dependent patterns.
Heart and lungs: what happens to the cardiovascular and respiratory systems
The most robust acute effect is dose-dependent tachycardia. Following consumption, the risk of myocardial infarction increases approximately 4,8 times during the first hour in susceptible adults, and there are reports of arrhythmias (e.g., atrial fibrillation) and transient cerebrovascular events. In the elderly or those with heart disease, the increase in catecholamines, cardiac workload, and carboxyhemoglobin may elevate risks, including marked orthostatic hypotension.
In the respiratory system, acute bronchodilation is observed. However, chronic combustion is associated with airway irritation, a higher prevalence of bronchitis (cough and sputum production), and endoscopic and histopathological findings consistent with damage. Cannabis smoke shares thousands of compounds with tobacco smoke, with different toxicant profiles (e.g., more ammonia or hydrogen cyanide in some measurements, fewer other carcinogens in comparison), and although the relationship with lung cancer is debated, exposure to combustion products are not harmless.
Immune and endocrine system
In chronic users, changes in the expression of cannabinoid receptors in leukocytes and immunomodulatory signals have been described, with possible decreases in antitumor defenses and alterations in alveolar macrophages. In experimental models, THC can suppress T cell response; some studies hypothesize about its role in the immunity of seropositive peopleHowever, more robust evidence is needed.
At the endocrine level, cannabinoids alter the hypothalamic-pituitary-adrenal axis and sex hormones, with inhibitory effects on desire and arousal, and a potential impact on fertility. Furthermore, a transient decrease in adrenaline and noradrenaline in the adrenal medulla has been observed following acute THC use, which disappears with repeated use.
Driving and safety: perception vs reality
A common belief is that “driving slower” compensates for the impairment caused by cannabis. The evidence does not support this. Several reviews show that the risk of accidents increases (in some analyses, it almost doubles in the first few hours), with deficits in tracking, lane control, reaction times, and sustained attention. Even if the driver tries to compensate, these deficits emerge in unforeseen situations. clear performance limitations.
Practical rules: avoid driving, cycling, or operating machinery while the effects last—longer if consumed orally. Combining it with alcohol is especially dangerous, and experimental data indicates that alcohol can accelerate THC absorption, enhancing the effects. psychoactive effect and deterioration.
Dosage, routes and toxicity: what you should know
No direct deaths from cannabis overdose have been documented under typical consumption conditions, and the lethal toxicity of THC is very low (lethal doses in the laboratory are extremely high). This does not mean that consumption is harmless: there are serious conditions such as cannabinoid hyperemesis syndrome (CHS), with uncontrollable vomiting in chronic users that improves with hot baths and resolves with abstinence. Other conditions have also been described. cases of pancreatitis associated with use.
Contamination of cannabis with molds (Aspergillus spp.) or other pathogens (e.g., Salmonella) can lead to opportunistic infections or poisoning. In clinical settings, practices such as heating the material to 150°C for a few minutes to inactivate spores, while avoiding THC degradation, have been recommended; however, the most prudent approach is Do not consume moldy or poorly preserved material.
Pregnancy and development
Evidence in humans is still limited, but there are signs of an association between prenatal exposure and reduced fetal growth, miscarriages, and deficits in language, attention, and cognitive performance later in life, as well as problematic behaviors in adolescence. Cannabinoids are considered to interfere with the endocannabinoid system during development, so their use in Pregnancy is not recommended.
Individual factors: sex, genetics, and expectations
Sex differences are beginning to emerge: in some studies, men show more deficits in memory and object recognition, while women exhibit more problems with attention and executive functions. These differences persist even when controlling for variables such as alcohol and nicotine, state anxiety, personality traits, and compulsive behaviors.
Expectations also play a role: consumers tend to expect more positive effects (relaxation, laughter, sociability) and fewer negative ones, which reinforces usage; non-consumers focus more on adverse consequences. Experience shows that the same subjective effect can be experienced as pleasant or unpleasant depending on the context, the dose, and the history of consumption.
Added risks: polydrug use and “fake marijuana”
Cannabis is rarely used alone: national surveys show high rates of co-use with alcohol and other recreational drugs, which complicates risk analysis and makes functional impairment more likely. Polysubstance use means a greater likelihood of adverse effects and of risky behaviors.
Meanwhile, so-called “synthetic marijuana” (laboratory-produced cannabinoids sprayed onto plant material) does not contain natural THC and has a worse safety profile: unpredictable effects, serious reactions, and a more intense and prolonged withdrawal syndrome than that of products containing THC. Regulation is minimal, and its composition... highly variable between batches.
How to quit or reduce the damage if you decide to continue
Identifying triggers (stress, boredom, social situations) and signs of dependence (need to increase doses, abandonment of activities, relationship conflicts) is a first step. Keeping a journal of consumption and mood, practicing mindfulness, and setting specific monthly goals are tools that help in recovery. feeling of control.
In professional treatment, cognitive-behavioral therapy, support groups, and structured detoxification programs have shown effectiveness. For withdrawal management, some medications have been studied with mixed results; dronabinol (pharmaceutical THC) has shown utility in certain clinical cases, always under supervision. Seeking specialized help reduces relapses and provides personalized strategies and emotional support.
If you or someone close to you ever experience severe symptoms after consuming edibles (extreme confusion, panic, rapid heart palpitations, hallucinations, persistent vomiting), you should contact poison control services or go to the emergency room. With edibles, remember that the peak effect can take up to 4 hours; avoid redosing out of impatience and never... mix with alcohol if you are going to do risky activities.
The available science paints a nuanced picture: cannabis produces subjective effects valued by many users (relaxation, laughter, heightened sensory appreciation), but it carries real risks that increase with the dose, frequency, potency of the product, and individual vulnerability. Variables such as age of initiation, expectations, mixing with other substances, route of administration, and social context mean that the experience varies from person to person; understanding these nuances allows for minimizing harm, recognizing warning signs, and making more informed decisions. Information and prudence.
