WASHINGTON -- Chronic marijuana use by teenage boys does not appear to be linked to later physical or mental health issues such as depression, psychotic symptoms or asthma, according to a study published by the American Psychological Association. 
 
 Researchers from the University of Pittsburgh Medical Center and Rutgers University tracked 408 males from adolescence into their mid-30s for the study, which was published in Psychology of Addictive Behaviors. 
 
 "What we found was a little surprising," said lead researcher Jordan Bechtold, PhD, a psychology research fellow at the University of Pittsburgh Medical Center. "There were no differences in any of the mental or physical health outcomes that we measured regardless of the amount or frequency of marijuana used during adolescence." 
 
 Marijuana use has undergone intense scrutiny as several states and the District of Columbia have legalized the drug, prompting the researchers to examine whether teen marijuana use has long-term health consequences. Based on some prior studies, they expected to find a link between teen marijuana use and the later development of psychotic symptoms (delusions, hallucinations, etc.), cancer, asthma or respiratory problems, but they found none. The study also found no link between teen marijuana use and lifetime depression, anxiety, allergies, headaches or high blood pressure. This study is one of just a few studies on the long-term health effects of teen marijuana use that have tracked hundreds of participants for more than two decades of their lives, Bechtold said. 
 
 The research was an offshoot of the Pittsburgh Youth Study, which began tracking 14-year-old male Pittsburgh public school students in the late 1980s to analyze various health and social issues. For 12 years, participants were surveyed annually or semiannually, and a follow-up survey was conducted with 408 participants in 2009-10 when they were 36 years old. The study sample was 54 percent black, 42 percent white and 4 percent other races or ethnicities. There were no differences in the findings based on race or ethnicity. 
 
 Participants were divided into four groups based on their reported marijuana use: low or non-users (46 percent); early chronic users (22 percent); participants who only smoked marijuana during adolescence (11 percent); and those who began using marijuana later in their teen years and continued using the drug (21 percent). Early chronic users reported much higher marijuana use, which rapidly increased during their teens to a peak of more than 200 days per year on average when they were 22 years old. Their marijuana use then declined somewhat as they got older. 
 
 The researchers controlled for other factors that could have influenced the findings, including cigarette smoking, other illicit drug use, and participants' access to health insurance. Since the study included only males, there were no findings or conclusions about women. Relatively few participants had psychotic symptoms, according to the study. 
 
 "We wanted to help inform the debate about legalization of marijuana, but it's a very complicated issue and one study should not be taken in isolation," Bechtold said. 
 
 ### 
 
 Article: "Chronic Adolescent Marijuana Use as a Risk Factor for Physical and Mental Health Problems in Young Adult Men;" Jordan Bechtold, PhD, and Dustin Pardini, PhD University of Pittsburgh Medical Center; Theresa Simpson, MA, and Helene R. White, PhD; Rutgers University; Psychology of Addictive Behaviors; published online Aug. 3, 2015. 
 
 Full text of the article is available from the APA Public Affairs Office and at 
 
 http://www. apa. org/ pubs/ journals/ releases/ adb-adb0000103. pdf . 
 
 Contact: Jordan Bechtold at beardsleejb@upmc.edu or (949) 291-7520. 
 
 The American Psychological Association, in Washington, D.C., is the largest scientific and professional organization representing psychology in the United States. APA's membership includes more than 122,500 researchers, educators, clinicians, consultants and students. Through its divisions in 54 subfields of psychology and affiliations with 60 state, territorial and Canadian provincial associations, APA works to advance the creation, communication and application of psychological knowledge to benefit society and improve people's lives. 
 
 http://www. apa. org 
 
 If you do not want to receive APA news releases, please let us know at public.affairs@apa.org or 202-336-5700. ||||| A comprehensive analysis of more than 400 men over a 20-year period casts new doubt on the idea of marijuana use, even when long-term, being associated with physical and mental health problems later on in life. 
 
 The authors of the study, published in Psychology of Addictive Behaviors, looked at data taken from the Pittsburgh Youth Study (PYS), a longitudinal study that attempted to track the development of antisocial and delinquent behavior among a selected group of first, third, and seventh grade boys attending public school in Pittsburgh from 1987 to 1988 (For the purposes of this current study, only data on the seventh grade boys, totaling 506 kids, was used). 
 
 Half of the original group was selected because they represented the top 30 percent of those with reported conduct issues, while the other half was randomly picked from the class roster. Slightly more than half of the group was identified as black and the other half as white. 
 
 For 10 years, PYS researchers conducted regular follow-up interviews with these boys, first semiannually in their teens, and then annually until they turned 25. When they became 35 in 2010, the researchers subjected them to one last interview, with about 82 percent of those still living showing up for the occasion. 
 
 Because of the meticulous record-keeping by the PYS, the current authors were able to reliably track not only how healthy these boys were as they matured, but also their frequency of marijuana use over time. They ultimately divided the subjects into one of four groups: Those who rarely or never used marijuana (46 percent); those who mostly used it in their teens (11 percent); those who took up the habit in adulthood (21 percent); and those who started early and become chronic — pun intended — pot users as they grew up (22 percent). They then compared the health status of these groups to one another, controlling for factors like tobacco use and socioeconomic status. 
 
 “[F]indings from this sample indicated that chronic marijuana users were not more likely than late increasing users, adolescence-limited users, or low/nonusers to experience several physical or mental health problems in their mid-30s,” they wrote. “In fact, there were no significant differences between marijuana trajectory groups in terms of adult health outcomes, even when models were run without controlling for potential confounds.” 
 
 As the researchers note, their results are somewhat surprising, flying in the face of previous studies that have found a small but real link between chronic marijuana use to the development of psychological issues like depression or schizophrenia, while reaffirming several other studies that found the opposite. In many ways, though, this study stands unique by being able to measure the health of its subjects as they grew up, rather than by looking back and asking people to remember when they first became sick or how much marijuana they once used when they were younger. 
 
 Research attempting to study the links between long-term marijuana use and actual health problems have largely been inconsistent, even if the reasoning behind a connection makes sense, such as with marijuana smoke being carcinogenic. 
 
 And even this latest study doesn’t come without its flaws. For one, only men were studied; only for 20 years, before the onset of conditions like cardiovascular disease; and only for certain diagnosable and self-reported health conditions. Maybe there isn’t a real association between depression and long-term marijuana use, but there could be one for less rigid symptoms like an increased sense of paranoia. 
 
 And the researchers theorize that maybe it’s a subset of people who are susceptible to the negative effects of long-term pot. “[I]t is increasingly being recognized that individual differences likely moderate the association between marijuana use and psychotic disorders,” they wrote. “For example, some studies have found that genetic liability affects whether, for whom, and the extent to which, marijuana has a negative influence on mental health.” 
 
 Similarly, other research suggests that marijuana doesn’t actually cause but rather accelerates the development of disorders like schizophrenia. 
 
 All of which is to say that this study, as the researchers themselves admit, isn’t the definitive answer to whether marijuana should become fully legalized, though it certainly is important. 
 
 “Indeed, marijuana policymakers and stakeholders need to consider the results of any single study in the context of the larger body of work on the potential adverse consequences of early onset chronic marijuana use,” they concluded. 
 
 Source: Bechtold J, Simpson T, White H, et al. Chronic Adolescent Marijuana Use as a Risk Factor for Physical and Mental Health Problems in Young Adult Men. Psychology of Addictive Behaviors. 2015. ||||| A still from "Reefer Madness," an anti-marijuana propaganda film from 1936. 
 
 You may have read this week that a new "20-year research study" on marijuana use "finally demolishes claims that smoking marijuana is harmless," and has found that it "makes you stupid," that "smoking marijuana over the long-term can develop cancer" [SIC], and that marijuana is "as addictive as heroin." At least, that's what you'd conclude if you'd read most media coverage of the study. But if you'd actually read the study yourself (which I highly recommend!), you'd likely walk away with very different conclusions. 
 
 The paper in question is a review of 20 years of existing research into the health effects of marijuana use. By design, it doesn't tell us anything we don't already know. The focus is almost exclusively on the effects of long-term heavy (daily or near-daily) marijuana use: "this paper deals with the adverse effects of cannabis smoking, especially the adverse health effects of regular, typically daily, cannabis smoking," the author, Wayne Hall, a drug adviser to the World Health Organization, writes. 
 
 Setting aside the alarmist accounts of the study in many media outlets, here's what Hall actually found: 
 
 You can't OD from marijuana 
 
 "The estimated fatal dose [of THC, the primary active compound in marijuana] in humans derived from animal studies is between 15 and 70 grams. This is a far greater amount of cannabis that even a very heavy cannabis user could use in a day," Hall writes. The average joint contains about a half a gram of marijuana, and the average potency of seized marijuana in 2013 was 12.58 percent, which means there are about 0.06 grams of THC in the average joint, which means that somebody would need to smoke somewhere between 238 and 1,113 joints in a day - or at least 10 joints an hour, for 24 hours straight - before overdose could become a realistic concern. 
 
 Don't drive stoned 
 
 Stoned driving is considerably safer than drunk driving, but it's still a dumb thing to do, Hall writes. "Cannabis users who drive while intoxicated increase their risk of motor vehicle crashes 2–3 times as against 6–15 times for comparable intoxicating doses of alcohol." 
 
 Don't smoke weed while you're pregnant 
 
 Studies have demonstrated a link between marijuana use during pregnancy and low birth weight, "although the effect was smaller than that for tobacco smoking," Hill notes. There is some evidence of a link between prenatal cannabis exposure and a variety of problems later in life, like lower IQ and behavioral problems. But, "uncertainty remains because of the small number of studies, the small samples of women in each and the researchers’ limited ability to control for the confounding effects of other drug use during pregnancy, maternal drug use post-birth and poor parenting." 
 
 In short, "it is prudent to counsel women against using cannabis during pregnancy," Hall concludes. 
 
 You can get addicted to marijuana, but it's highly unlikely 
 
 People who try marijuana are significantly less likely to become dependent on it than users of just about any other drug, including tobacco, heroin, cocaine, alcohol or stimulants: "The life-time risk of developing dependence among those who have ever used cannabis was estimated at 9% in the United States in the early 1990s as against 32% for nicotine, 23% for heroin, 17% for cocaine, 15% for alcohol and 11% for stimulants." More than nine-in-ten people who try marijuana don't get addicted to it. 
 
 The risk of addiction is higher (one-in-six) if you start using in your teens. Dependent users can experience withdrawal symptoms when they quit, including "anxiety, insomnia, appetite disturbance and depression." That said, "The adverse health and social consequences of cannabis use reported by cannabis users who seek treatment for dependence appear to be less severe than those reported by alcohol and opioid-dependent people," Hall writes. 
 
 There's some evidence that heavy marijuana use can lead to cognitive impairment, particularly if you start in your teens 
 
 Some studies have found deficits in learning and attention among regular marijuana users, but "it still remains unclear whether cognitive function recovers fully after cessation of longterm cannabis use." One particularly well-known study posited a link between IQ declines and teen marijuana use, but other research has contested that claim. 
 
 There may be a link between heavy teen marijuana use and lower educational attainment, but again the causality is far from clear 
 
 A recent study concluded that heavy marijuana use in your teens decreases your likelihood of graduating high school, but as I noted at the time, there could be any number of confounding factors contributing to this finding. Hall notes that "An analysis of twins who were discordant for early cannabis use [e.g., one used while the other didn't] found no difference in risk of early school-leaving between the twins who did and did not use cannabis, suggesting that the association was explained by shared genetic and environmental risk factors. These findings are supported by two earlier analyses of US twin-study data." 
 
 There may be links between teen marijuana use and the use of harder drugs, but this research is hotly contested 
 
 Studies show some evidence for the so-called "gateway theory," but according to Hall "we don't know whether the link is causal." Many researchers suspect that to the extent there is a gateway drug, it's tobacco, not marijuana. 
 
 There is some evidence that marijuana use doubles the likelihood of developing a psychosis 
 
 But, "it is difficult to decide whether cannabis use has had any effects on psychosis incidence, because even if the relationship were causal, cannabis use would produce a very modest increase in [overall] incidence," Hall writes. It nevertheless seems prudent to suggest that if you have pre-existing mental conditions and decide to use marijuana (or alcohol or any other drug, for that matter), you're rolling the dice when it comes to your mental health. 
 
 There's no good evidence of a link between marijuana use and depression, but some evidence of a link with suicide. 
 
 Some studies have suggested a weak link between marijuana use and depression, but those links disappear after you adjust for confounding factors. There seems to be better evidence for connections between marijuana and increased risk of suicide, but several analyses of these studies suggest "that these studies and measures used were too varied to quantify risk meaningfully, and most of the studies had not excluded reverse causation or controlled adequately for confounding," Hall writes. 
 
 Regular marijuana use is linked to increased risk of chronic bronchitis 
 
 Yes, inhaling flaming plant material into your lungs on a regular basis could impair your respiratory function. 
 
 Marijuana smoking probably increases the risk of heart attack in middle aged adults 
 
 Among middle-aged and older adults, there is evidence of increased risk of heart attack in the hour or so after smoking marijuana. There is also limited evidence that smoking marijuana may provoke cardiovascular events in young people with undiagnosed cardiovascular disease. 
 
 There may be a link between marijuana use and testicular cancer in men 
 
 "Studies found a doubling of risk of non-seminoma testicular tumours among cannabis users and suggestive evidence that risk increased with earlier initiation and more frequent use of cannabis," Hall writes. "It is also a biologically plausible effect, given that cannabinoid receptors are found in the male reproductive system." 
 
 Overall 
 
 The overall take-home message from Hall can be summed up as follows: if you use marijuana, don't overdo it. If you're a teen or a pregnant lady, best not to use marijuana at all. 
 
 It's important to note that any effects noted above are primarily among heavy, long-term users. Long-term use of any drug - be it marijuana, alcohol or nicotine - will come with negative health consequences, even if, according to this paper, the consequences are not as bad with marijuana use.
– Previous studies have found teen marijuana use could result in cancer, asthma, respiratory problems, and psychotic symptoms like delusions and hallucinations over time. That's why researchers say the results of a new long-term study following teen pot smokers into their 30s are "a little surprising." Researchers who analyzed 408 males for health and social issues from age 14 to 26, then checked back in with the participants at age 36, found no connection between pot use and any of the aforementioned conditions. Not only that, the study in Psychology of Addictive Behaviors—an extension of the Pittsburgh Youth Study of the 1980s—also found no apparent link between smoking marijuana as a teen and later depression, anxiety, allergies, headaches, or high blood pressure, according to a press release. The participants—54% black, 42% white—were classed into four groups: those who rarely or never used marijuana (46%); chronic users who started using the drug early (22%); those who picked up the habit as an adult (21%); and those who smoked marijuana only in their youth (11%). "There were no differences in any of the mental or physical health outcomes that we measured regardless of the amount or frequency of marijuana used during adolescence," a researcher explains. That means chronic users who smoked the drug 200 days a year on average at age 22 were no more likely to have health problems than those who rarely or never picked up a joint. Researchers say the study should "help inform the debate about legalization of marijuana," but "should not be taken in isolation" as negative health effects may appear in those with a genetic liability, per Medical Daily. (Marijuana apparently heals broken bones.)