Fear-mongering headlines claiming that marijuana use causes birth defects, heart-attacks, and psychosis are common in the mainstream media. But newly published scientific evidence makes it clear that what is often portrayed as ‘conventional wisdom’ is really nothing more than ‘reefer madness.’

Pot Not Likely to Make You Psychotic

There exists “minimal evidence” to support an association between cannabis use alone and the onset of psychotic symptoms in young people, according to data published online in March in the Journal of Adolescent Health.

Investigators from the University of Pennsylvania, Department of Psychiatry assessed the relationship between drug use and the onset of psychotic symptoms in a cohort of 4,171 young people ages 14 to 21. Authors reported that “neither frequent nor early cannabis use predicted increased odds of psychosis spectrum classification” after researchers adjusted for potential confounders (e.g., concurrent use of other substances, comorbid psychopathology, and trauma exposure).

They concluded, “Overall, we found minimal evidence for associations between cannabis use by itself and psychosis spectrum symptoms.”

They’re not alone. In fact, the only other US-based longitudinal study to assess early onset cannabis use and mental health similarly reported that exposure is not positively associated with a greater risk of psychosis or other psychiatric health disorders later in life.

Do some individuals with psychiatric disorders smoke pot? Of course. But according to a 2016 literature review, this association exists because many individuals predisposed to psychosis are simply more likely to experiment with weed at an early age as compared to those who are not. “Evidence reviewed here suggests that cannabis does not in itself cause a psychosis disorder,” researchers concluded. “Rather, the evidence leads us to conclude that both early use and heavy use of cannabis are more likely in individuals with a vulnerability to psychosis.”

Maternal Marijuana Use Isn’t Independently Associated With Adverse Neurodevelopment

Federal statistics indicate that between four and five percent of pregnant women report using pot during pregnancy, sometimes as a remedy for morning sickness. However, even in states where cannabis use is legal, such behavior may result in involvement with child welfare services and other punitive legal actions — a stance that is predicated on the belief that maternal cannabis use inherently poses significant health risks to the child. But a just published scientific review in the journal Preventive Medicine challenges this long held contention.

A pair of researchers from the University of Maryland, Department of Obstetrics, Gynecology and Reproductive Sciences and the Virginia Commonwealth University, Department of Obstetrics and Gynecology and Psychiatry reviewed four prospective cohort studies evaluating the long-term health outcomes of in utero cannabis exposure. They concluded, “The evidence base for maternal-infant health outcomes of cannabis use in pregnancy is more robust than for many other substances. … Although there is a theoretical potential for cannabis to interfere with neurodevelopment, human data drawn from [these] four prospective cohorts have not identified any long-term or long lasting meaningful differences between children exposed in utero to cannabis and those not.”

Other recent studies similarly allay fears regarding marijuana exposure during pregnancy. For example, a 2016 literature review published in the journal Obstetrics & Gynecology reported that the moderate use of cannabis during pregnancy is not an independent risk factor for adverse neonatal outcomes such as low birth weight, and a 2017 study reports that neither maternal nor paternal pot use is independently associated with adverse effects on children’s educational attainment. By contrast, researchers determined that maternal alcohol use was associated with detrimental educational outcomes.

Smoking Pot Likely Isn’t Going to Trigger a Heart Attack

Consuming marijuana increases one’s risk of heart problems “and may even prove fatal for young and middle-aged users.” So declared the United Kingdom’s Daily Mail in 2014 in typically hysterical fashion. But the results of recently published 25-year longitudinal study conclude that young adults who smoke pot are at no greater risk of myocardial infarction or other adverse cardiovascular problems as compared to non-users.

Writing in April in the American Journal of Public Health, an international team of researchers from the United States and Switzerland assessed cumulative cannabis use and cardiovascular risk in a cohort of over 5,000 subjects over a period of more than two decades. Authors reported, "Compared with no marijuana use, cumulative lifetime and recent marijuana use showed no association with incident CVD (cardiovascular disease), stroke or transient ischemic attacks, coronary heart disease, or CVD mortality."