Cannabis
How It Works
- THCⓘ
- CBDⓘ
- Effects vary hugely based on strain, dose, individual, and method of use
Known Risks
- Heavy cannabis use may increase psychosis risk[3]
- Impairs memory and learning, especially with early/heavy use
- Addiction occurs in about 9% of users (higher if starting as teen)ⓘ
- Driving impaired by cannabis is dangerous[5]
Medical Use
- Medical cannabis has legitimate uses but is often overhyped[6]
- Strongest evidence: chemotherapy nausea, certain epilepsy, chronic painⓘ
- Weak evidence: many other claimed benefits
- Cannabinoid hyperemesis syndromeⓘ
MDMA (Ecstasy)
How It Works
- MDMAⓘ
- Causes massive serotonin release (the "comedown" is serotonin depletion)
- Often sold mixed with other substances
Known Risks
- Regular MDMA use is associated with lasting memory impairment[10]
- Brain changes may be long-lasting[11]
- Hyperthermia and dehydration can be fatal (but over-drinking water is also dangerous)
- Serotonin syndromeⓘ
Harm Reduction
- Test substances (many "ecstasy" pills contain other drugs)
- Do not combine with antidepressants (SSRIs, MAOIs)
- Stay cool, drink water moderately (not excessively)
- Long breaks between uses may reduce neurotoxicity
Opioids
How They Work
- Opioidⓘ
- Extremely effective for pain, extremely addictive
- Tolerance develops quickly, requiring higher doses
Overdose Risk
- Opioids kill by stopping breathing[14]
- Fentanylⓘ
- Mixing with alcohol or benzodiazepines greatly increases risk
- Naloxone (Narcan)ⓘ
Treatment
- Methadone treatment requires careful dosing[17]
- Medication-assisted treatment (methadone, buprenorphine) is most effective approach
- "Detox only" approaches have very high relapse rates
Cocaine
How It Works
- Cocaineⓘ
- Extremely short high encourages compulsive redosing
- Crack cocaine is same drug, different form (smoked = faster/more intense)
Known Risks
- Cocaine causes serious cardiovascular damage[19]
- Heart attack risk even in young, healthy users
- Stroke risk significantly elevated
- Nasal septum damage from snorting
- Highly psychologically addictive
Stimulants (Amphetamines/Methamphetamine)
How They Work
- Amphetamineⓘ
- Methamphetamineⓘ
- Meth is neurotoxic in ways prescription amphetamines generally are not
Known Risks
- Stimulant use causes measurable brain changes[22]
- Limited effective treatments exist[23]
- Severe dental problems ("meth mouth")
- Psychosis with heavy use
- Sleep deprivation effects compound over time
Psychedelics
How They Work
- Psilocybinⓘ
- LSDⓘ
- Generally not physically addictive
- Set and settingⓘ
Therapeutic Potential
- Psilocybin shows promise for depression and anxiety[27]
- Research ongoing for addiction, PTSD, depression
- Not yet approved for general use (clinical trials only)
Risks
- Psychological distress during experience ("bad trip")
- HPPDⓘ
- Can trigger psychotic episodes in vulnerable individuals
- No physical overdose risk, but accidents from impaired judgment
Nicotine
How It Works
- Nicotineⓘ
- One of the most addictive substances known
- Withdrawal causes irritability, anxiety, difficulty concentrating
Health Effects
- Nicotine dependence linked to depression and anxiety[30]
- Cigarettes kill through tar, carbon monoxide, and combustion products—not nicotine directly
- Nicotine replacement (patches, gum) much safer than smoking
- Vaping is less harmful than smoking but not harmless[31]
Quitting
- Combination of nicotine replacement + behavioral support most effective
- Medications (varenicline, bupropion) can help
- Most smokers try to quit multiple times before succeeding
General Harm Reduction
Testing Substances
- Street drugs often contain unexpected substances
- Fentanyl contamination is increasingly common
- Drug checking services exist in some areas
Mixing Drugs
Warning: Combining depressants (alcohol, opioids, benzodiazepines) greatly increases overdose risk
Warning: Stimulants can mask alcohol's effects, leading to alcohol poisoning
Warning: MDMA + antidepressants = serotonin syndrome risk
Getting Help
- Treatment works but often requires multiple attempts
- Harm reduction services (needle exchanges, supervised consumption) save lives
- See our [addiction page](/addiction) for more information
---
References
- Hall W, Degenhardt L (2009). Should Burden of Disease Estimates Include Cannabis Use as a Risk Factor for Psychosis?. PLOS Medicine. [DOI]
- Yeung M, et al. (2024). A quantitative projection of the net health effects of cannabis legalization in the US. PLOS ONE. [DOI]
- MacCallum CA, et al. (2022). Lessons from 20 years of medical cannabis use in Canada. PLOS ONE. [DOI]
- Murphy PN, et al. (2016). Verbal Memory Impairment in Polydrug Ecstasy Users: A Clinical Perspective. PLOS ONE. [DOI]
- Kish SJ, et al. (2012). The Effects of Ecstasy (MDMA) on Brain Serotonin Transporters Are Dependent on Age-of-First Exposure. PLOS ONE. [DOI]
- White JM, Irvine RJ (2015). Understanding Heroin Overdose: A Study of the Acute Respiratory Depressant Effects of Injected Pharmaceutical Heroin. PLOS ONE. [DOI]
- Eap CB, et al. (2006). Determining Effective Methadone Doses for Individual Opioid-Dependent Patients. PLOS Medicine. [DOI]
- Rocha BA, et al. (2014). Cardiovascular Complications following Chronic Treatment with Cocaine and Testosterone in Adolescent Rats. PLOS ONE. [DOI]
- Todd G, et al. (2013). Illicit Stimulant Use Is Associated with Abnormal Substantia Nigra Morphology in Humans. PLOS ONE. [DOI]
- Ronsley C, et al. (2020). Treatment of stimulant use disorder: A systematic review of reviews. PLOS ONE. [DOI]
- Ross S, et al. (2024). Psilocybin-assisted group psychotherapy and mindfulness-based stress reduction for treatment of cancer-related psychological distress. PLOS Medicine. [DOI]
- Mathew AR, et al. (2020). A key indicator of nicotine dependence is associated with greater depression and anxiety. PLOS ONE. [DOI]
- Harlow AF, et al. (2025). Patterns of e-cigarette use and interest in cessation among current users. PLOS ONE. [DOI]