The deleterious effects of cannabis during pregnancy on neonatal outcomes
Objectives: To evaluate whether cannabis use during pregnancy is associated with adverse neonatal outcomes that are independent of cigarette smoking.
Design: Prospective cohort study.
Setting: Adelaide (Australia), Auckland (New Zealand), Cork (Ireland), and Leeds, London and Manchester (United Kingdom).
Participants: 5610 pregnant nulliparous women with low risk pregnancies recruited for the Screening for Pregnancy Endpoints (SCOPE) study, November 2004 – February 2011. At 14–16 weeks of pregnancy, women were grouped by self‐reported cannabis use.
Main outcome measures: Infant birthweight, head circumference, birth length, gestational age, and severe neonatal morbidity or mortality.
Results: 314 women (5.6%) reported using cannabis in the 3 months before or during their pregnancy; 97 (31%) stopped using it before and 157 (50%) during the first 15 weeks of pregnancy, while 60 (19%) were still using cannabis at 15 weeks. Compared with babies of mother who had never used cannabis, infants of those who still used it at 15 weeks had lower mean values for birthweight (adjusted mean difference [aMD], –127 g; 95% CI, –238 to –17 g), head circumference (aMD, –0.5 cm; 95% CI, –0.8 to –0.1 cm), birth length (aMD, –0.8 cm; 95% CI, –1.4 to –0.2 cm), and gestational age at birth (aMD, –8.1 days; 95% CI, –12.1 to –4.0 days). The differences for all outcomes except gestational age were greater for women who used cannabis more than once a week than for those who used it less frequently.
Conclusions: Continuing to use cannabis during pregnancy is an independent risk factor for poorer neonatal outcomes.
The known: Cannabis is the illicit drug most widely used by women of reproductive age in Australia, but the effects of its use during pregnancy on neonatal outcomes are unclear.
The new: In our international cohort study, continued use of cannabis at 15 weeks of pregnancy was associated with significantly lower birthweight, head circumference, birth length, and gestational age at birth, as well as with more frequent severe neonatal morbidity or death.
The implications: We provide evidence for the negative impact of cannabis use by pregnant women on important neonatal outcomes, and that this impact is independent of tobacco use.
Cannabis is the most frequently used illicit drug in Australia, probably because of its increasing social and medical acceptance, as well as the recent legalisation of cannabis use in many parts of the world.1
According to the 2016 National Drug Strategy Household Survey, more than 10% of women of reproductive age had used cannabis during the preceding 12 months.2 The findings of studies evaluating neonatal outcomes associated with cannabis use by women during pregnancy have been mixed.3 , 4 A recent meta‐analysis found a significant association between prenatal cannabis exposure and reduced birthweight, as well as increased risk for infants of admission to intensive care.4 Many studies, however, did not take concurrent cigarette smoking or other illicit substance use into account, and some did not report the time or frequency of cannabis exposure. The largest and most recent study of self‐reported cannabis use during pregnancy found increased risks of pre‐term birth (adjusted risk ratio [aRR], 1.41, 95% confidence interval [CI], 1.36–1.47), small‐for‐gestational age (aRR, 1.41, 95% CI, 1.36–1.45), and neonatal intensive care unit admission (aRR, 1.40; 95% CI, 1.36–1.44).5 Once again, however, the number of cigarettes smoked each day and the time and duration of cannabis use were not assessed.
High quality information about the effect of cannabis use during pregnancy on important neonatal outcomes linked to immediate and long term health and wellbeing is needed for informing clinical practice and improving the education of women and health care providers about the potential risks. The aim of our study was therefore to assess associations between duration and frequency of cannabis use during pregnancy on infant birthweight, head circumference, birth length, gestational age, and neonatal morbidity and mortality.
The primary aim of the Screening for Pregnancy Endpoints (SCOPE) study, a multicentre prospective cohort study, is to develop screening tests for predicting pre‐eclampsia, spontaneous pre‐term birth, and small for gestational age babies.6 A total of 5628 nulliparous women without common risk factors for pregnancy complications were recruited between November 2004 and February 2011 in Adelaide (Australia), Auckland (New Zealand), Cork (Ireland), and Leeds, London and Manchester (United Kingdom).7 Research midwives collected information on demographic and lifestyle characteristics and medical history from participants at 14–16 weeks of pregnancy. Women were excluded from our analysis if their pregnancy ended earlier than 20 weeks (Supporting Information, figure).
Cannabis use by participants
The research nurse asked women about the duration and frequency of cannabis use from 3 months before until 15 weeks into their pregnancy. Women were allocated to four categories: never used cannabis, used cannabis but quit before pregnancy, used cannabis but quit during early pregnancy (by 15 weeks), and continued to use cannabis at 15 weeks of pregnancy. Women were also classified according to whether they used cannabis up to once or more than once a week, consistent with previous studies.8 , 9 We did not quantify the amount or strength of cannabis consumed.
Other variables assessed
Self‐reported smoking status was classified as never smoked, quit before pregnancy, quit during early pregnancy (by 15 weeks), and continued use at 15 weeks; for women still smoking, the number of cigarettes smoked was recorded. Women who used illicit substances other than cannabis during pregnancy were included in a single group (the individual numbers were too small for separate analyses). Alcohol consumption was classified as never used, quit before pregnancy, quit during early pregnancy (by 15 weeks) and continued use at 15 weeks; binge alcohol consumption (at least 6 units of alcohol per drinking episode) during pregnancy was also recorded. Ethnic background was self‐reported as European origin or other. Socio‐economic status of participants was assessed with the socio‐economic index (SEI). Developed in New Zealand, the SEI is an optimally weighted combination of income and education variables, corrected for age; ranging from 10 to 90 points, a higher score indicates higher socio‐economic status.10 At the 15‐week interview, participants also completed a lifestyle questionnaire that included the short form of the State–Trait Anxiety Inventory11 and the Edinburgh postnatal depression scale.12
Anthropometric measurements (infant birthweight, head circumference, birth length) were recorded by research midwives within 72 hours of birth. Information about severe neonatal morbidity or death (as a composite outcome) were collected by research midwives from case notes after infants had been discharged from hospital. Serious morbidity was defined by the original SCOPE consortium for infants born pre‐term (earlier than 37 weeks’ gestation) as grade III or IV intraventricular haemorrhage, chronic lung disease (receiving oxygen at home, or at 36 weeks’ gestation if the baby was born before 32 weeks’ gestation), necrotising enterocolitis, retinopathy of prematurity (stage 3 or 4), sepsis (confirmed in blood or cerebrospinal fluid), or cystic periventricular leukomalacia; for infants born at term, serious morbidity included grade II or III hypoxic ischaemic encephalopathy, ventilation for more than 24 hours, admission to a neonatal unit for more than 4 days, an Apgar score at 5 minutes of less than 4, cord arterial pH below 7.0 or base excess of less than –15 mEq/L, and neonatal seizures.
We used causal diagrams (directed acyclic graphs) to guide our selection of covariates for analyses.13 Frequencies and descriptive statistics were expressed as numbers and proportions or as means with standard deviations (SDs). Medians with interquartile ranges (IQRs) were reported when continuous variables were not normally distributed.
Possible confounding maternal characteristics identified a priori included age, body mass index (BMI), SEI, ethnic background, cigarette smoking, study centre, alcohol use, binge alcohol consumption, illicit drug use, and symptoms of anxiety or depression at 15 weeks. Anthropometric outcomes were further adjusted for infant sex; birthweight, head circumference, and birth length were also adjusted for gestational age at birth (using fractional polynomials for gestational age).
Associations between duration and frequency of cannabis use during pregnancy and gestational age at birth, birthweight, head circumference, and birth length were evaluated by multivariable mixed effects linear regression. The association between duration of cannabis use during pregnancy and severe neonatal morbidity or death was evaluated by logistic regression. We used mixed effects models, with country as a random effect and other covariates as fixed effects. We evaluated the robustness of our findings to uncontrolled confounding by calculating E‐values14 for the associations between cannabis use and outcomes.
As the SEI has not been validated outside New Zealand, in sensitivity analyses we adjusted outcomes for alternative individual measures of socio‐economic status, including income (< $75 000, ≥ $75 000), education (no tertiary, tertiary education), and employment status (employed, unemployed, other: including homemaker or parent, student, disabled).
P < 0.05 (two‐tailed) was defined as statistically significant. All analyses were undertaken in Stata IC 14.
Ethics approval was obtained from the Northern X Regional Ethics Committee in New Zealand (reference, AKX/02/00/364), the Central Northern Adelaide Health Service Ethics of Human Research Committee in Australia (reference, REC 1712/5/2008), the South‐East Multi‐Centre Research Ethics Committee, St Thomas Hospital Research Ethics Committee, and Central Manchester Research Ethics Committee in the United Kingdom (reference, 06/MRE01/98), and the Clinical Research Ethics Committee of the Cork Teaching Hospitals in Ireland (reference, ECM5 (10) 05/02/08). The women involved in the study provided written informed consent for the analysis of their data.
After excluding 18 women whose pregnancies ended at less than 20 weeks’ gestation, 5610 women were included in our analysis (Supporting Information, figure), of whom 314 (5.6%) reported using cannabis before or during pregnancy; 97 (31%) had stopped using it before pregnancy, 157 (50%) had stopped by 15 weeks, and 60 (19%) continued to use cannabis at 15 weeks of pregnancy. The mean age and socio‐economic status of women who continued to use cannabis were lower, and their mean anxiety and depressive symptom scores higher than for other participants; the proportions who consumed alcohol, used other illicit drugs, or were smoking at 15 weeks of pregnancy were also higher (Box 1).
Neonatal outcomes: effect of cannabis use
Compared with the babies of women who had never used cannabis, the infants of women who continued to use cannabis at 15 weeks had lower mean values for birthweight (adjusted mean difference [aMD], –127 g; 95% CI, –238 to –17 g), head circumference (aMD, –0.5 cm; 95% CI, –0.8 to –0.1 cm), birth length (aMD, –0.8 cm; 95% CI, –1.4 to –0.2 cm), and gestational age (aMD, –8.1 days; 95% CI, –12.1 to –4.0 days). Neonatal outcomes for babies of women who quit before or during early pregnancy were not significantly different from those for infants of women who had never used cannabis (Box 2). The difference in birthweight associated with continued use of cannabis was similar to that for babies of mothers who smoked up to nine cigarettes per day (v never smoked during pregnancy: aMD, –104 g; 95% CI, –162 to –46 g) or more (aMD, –166 g, 95% CI, –219 to –112 g) at 15 weeks.
E‐values for the association between continued cannabis use and adverse perinatal outcomes ranged between 1.74 for birthweight and 2.58 for gestational age. This means that the risk ratio, after adjusting for measured covariates, for an unmeasured confounder associated with both cannabis use and the outcome would need to be 1.74 in the case of birthweight (corresponding to a reduction of about 350 g) or 2.58 in the case of gestational age (corresponding to a reduction of about 14 days) to reduce the aMDs associated with cannabis use to zero (Supporting Information, table 1).
Neonatal outcomes: effect of level of cannabis use during early pregnancy
Compared with the babies of women who used cannabis up to once a week during early pregnancy, the infants of women who used cannabis more than once a week had lower mean values for birthweight (aMD, –197 g; 95% CI, –334 to –60 g), head circumference (aMD, –0.9 cm; 95% CI, –1.3 to –0.5 cm), and birth length (aMD, –1.0 cm; –1.7 to –0.4 cm) (Box 3). The odds ratio for severe infant morbidity or death increased with persistence of cannabis use during pregnancy (for trend in adjusted odds ratio: P = 0.041) (Box 4).
Adjusting for individual markers of socio‐economic status (education status, employment status, income level) instead of SEI score did not substantially alter our findings (Supporting Information, table 2–4).
We report robust evidence that continued cannabis use during pregnancy is associated, independent of continued cigarette smoking, with significant reductions in infant gestational age at birth, birthweight and length, and head circumference, as well as increased frequency of severe neonatal morbidity. The observed reduction in neonatal birthweight was comparable with that associated with continued tobacco use during pregnancy. The outcomes for infants of women who had stopped using cannabis by 15 weeks of pregnancy did not differ from those of mothers who had never used cannabis. Our findings are of considerable public health importance, particularly given the increasing legal, social, and medical acceptance of cannabis, and they highlight the importance of health care providers counselling women of reproductive aged to stop or reduce cannabis use before becoming pregnant or, at the latest, early in pregnancy.
Our study was an extension of an earlier investigation, with the same cohort of women, of associations between cannabis use during pregnancy and major pregnancy complications.15 The earlier study identified that continued cannabis use during pregnancy was associated with increased risk of spontaneous pre‐term birth, but not with increased risks of small for gestational age babies, pre‐eclampsia, gestational hypertension, or gestational diabetes.15 Our study adds data on key neonatal outcomes, including differences according to frequency of cannabis use during pregnancy.
A recent meta‐analysis found that using cannabis during pregnancy was associated with reduced birthweight (pooled mean difference [pMD], –109 g; 95% CI, –180 to –39 g; ten studies), but not reduced gestational age at birth (pMD, –0.20 days; 95% CI, –0.62 to 0.22 days; five studies), birth length (pMD, –0.10 cm; 95% CI, –0.65 to 0.45 cm; six studies), or head circumference (pMD, –0.31 cm; 95% CI, –0.74 to 0.13 cm; six studies).4 Study heterogeneity (I 2 ) for the various outcomes ranged, however, between 33% and 97%. Further, pooled risk estimates were not adjusted for cigarette smoking, and growth outcomes were not adjusted for gestational age at birth. As many cannabis users also smoke or drink alcohol, isolating cannabis‐specific effects was therefore challenging. Another recent meta‐analysis found that cannabis use during pregnancy was associated with increased risks of low birthweight (risk ratio [RR], 1.43; 95% CI, 1.27–1.62; 12 studies) and pre‐term delivery (RR, 1.32; 95% CI, 1.14–1.54; 14 studies), but these differences were removed by adjusting for cigarette use and other confounders (low birthweight: adjusted RR, 1.16; 95% CI, 0.98–1.37 [four studies]; pre‐term birth: adjusted RR, 1.08; 95% CI, 0.82–1.43 [four studies]).3 In contrast, we found that cannabis use during pregnancy is an independent risk factor for poorer neonatal outcomes.
A few studies have examined associations between neonatal growth outcomes and the frequency8 , 9 or duration (first, second, third trimester)16 , 17 of cannabis use, or both.18 , 19 Our findings are consistent with those of three studies that found significant reductions in birthweight, head circumference, or birth length with increased frequency8 or duration of cannabis use during pregnancy;17 , 19 the other three studies found no differences.
We found that the frequency of severe neonatal morbidity and death was higher for babies of mothers who continued to use cannabis at 15 weeks, consistent with the results of a recent American study (adjusted odds ratio, 3.11; 95% CI, 1.40–6.91).20 These findings could reflect the lower gestational age at birth for babies of women who continue using cannabis during pregnancy or be related to altered fetal growth. How cannabis might impair fetal growth is unclear, but the effect may be related to the carbon monoxide generated by smoking cannabis.21 Alternatively, the effects might be mediated by maternal–placental–fetal neuroendocrine mechanisms, particularly by dysregulation of the diurnal cortisol cycle. A role for the endocannabinoid system in brain homeostasis has been described, and exogenous cannabinoids activate the hypothalamic–pituitary–adrenal axis.22 Cannabinoid administration dose‐dependently increases adrenocorticotropic hormone (ACTH) and cortisol concentrations in blood, but with chronic use tolerance rapidly develops.23 Further investigation of the neuroendocrine effects on mother and child of cannabis during pregnancy are warranted.
Strengths and limitations
Strengths of our secondary analysis included the prospective and rigorous collection of data on cannabis use during pregnancy (including its duration and frequency) by trained personnel, as well as on smoking, alcohol use, and the use of illicit substances. Limitations include the lack of information about the quantity of cannabis used and about how it was taken. The small numbers of women in the different categories of cannabis use during pregnancy limit the precision of our effect estimates. Further, data on the use and frequency of cannabis use during pregnancy relied on self‐reports, and we had no information at all about the second half of pregnancy. Nevertheless, self‐report has been found to reliably assess cannabis use during pregnancy in epidemiological studies.24 Any incomplete ascertainment of cannabis use would have been non‐systematic and therefore unrelated to the outcomes we investigated; further, misclassification of some users as non‐users would have diminished rather than amplified the reported associations.25 The E‐values for the reported associations indicate that a level of residual confounding sufficient to explain them seems unlikely. Finally, our findings were robust to different approaches to adjusting for socio‐economic status.
Our findings provide important information for women and health care providers about the potential harms of cannabis use during pregnancy. Continued and high frequency of cannabis use during pregnancy were each associated with significantly poorer neonatal outcomes. The long term effects on child health and development should be examined in further studies.
Box 1 – Characteristics of 5610 SCOPE study participants, 2004–2011, by cannabis use of mothers before and during pregnancy
How Long Does Withdrawal From Marijuana Last?
Steven Gans, MD is board-certified in psychiatry and is an active supervisor, teacher, and mentor at Massachusetts General Hospital.
Cannabis (marijuana) is the most commonly used illicit drug. For many years, marijuana has been considered a soft drug, exempt from the usual concerns about addiction. However, recent research has shown that cannabis withdrawal can and does occur when heavy pot smokers discontinue its use.
As a result, the diagnostic criteria for cannabis withdrawal is included in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5).
If you have been smoking pot heavily for at least a few months—whether as a regular pattern, in binges, or if you have become addicted—you may experience weed withdrawal if you abruptly stop using.
A Duke University study of 496 adult marijuana smokers who tried to quit found that 95.5% of them experienced at least one withdrawal symptom while 43.1% experienced more than one symptom. The number of symptoms the participants experienced was significantly linked to how often and how much the subjects smoked prior to trying to quit.
Those who were daily smokers experienced the most symptoms, but even those who reported using marijuana less than once a week experienced some withdrawal symptoms of moderate intensity.
Signs & Symptoms
Marijuana withdrawal symptoms are not life-threatening—their main danger is causing someone who really wants or needs to quit cannabis to relapse.
You might feel extra edgy and irritable, have trouble sleeping and eating, and may even get a stomachache or headache. Some people compare it to the feeling you get when you try to quit caffeine.
Although weed withdrawal typically lasts one to two weeks, some marijuana users experience several weeks or months of withdrawal symptoms, known as Post-Acute Withdrawal Syndrome (PAWS).
One person's experience of cannabis withdrawal might be quite different from another's, and the severity depends on a whole host of factors, including frequency of use as well as overall health. However, there are certain common withdrawal symptoms that usually occur within 24 to 72 hours of stopping heavy use.
Although many regular smokers of marijuana do not believe they are addicted to the drug, many former marijuana users report drug cravings in the early days of abstinence. The experience of cravings will vary from person to person, but tend to include a persistent desire to use the substance.
This is a hallmark of addiction, whether it's heroin, alcohol, gambling, or sex addiction. In one study, 75.7% of participants trying to quit reported an intense craving for marijuana.
Irritability can range from mild and relatively easy to control annoyance to excessive anger and even aggression. This is a normal reaction to withdrawing from marijuana.
If the irritability lasts for more than a week, it is a good idea to seek support from a doctor, drug counselor, or psychologist, as the symptom may be part of another issue that your cannabis use was masking.
More than half of those who try to quit marijuana report mood swings, irritability, or anxiety. Others report aggression, nervousness, restlessness, and a loss of concentration.
Anxiety can be a symptom of both cannabis intoxication and cannabis withdrawal. The distinctive paranoid feelings that occur when high on marijuana are well known among users,.
It can be worrying when anxiety continues or worsens even after you quit. As with the irritability, it can be helpful to remember that your fears are probably a natural part of drug withdrawal.
If you continue to feel anxious after a week of discontinuing cannabis, see a doctor. Cannabis use can sometimes cause substance-induced anxiety disorders, and there may have been an existing anxiety problem before you started using cannabis.
If you experience extended paranoia, especially if you also experience hallucinations or delusions, it is very important to be properly assessed by a mental health professional, ideally with expertise in substance issues such as an American Board of Addiction Medicine (ABAM)-certified physician or a psychiatrist.
Depression, characterized by a persistently sad mood accompanied by several other symptoms like decreased interest in daily activities and difficulty concentrating, is another possibility of cannabis withdrawal.
Occasional depressed feelings are natural. It is not unusual for people coming off cannabis to also become more aware of some of the negative consequences of their drug use as well as emotional states the marijuana has been masking.
For example, some people who cease marijuana after using for several years can feel they have wasted a considerable part of their life. These feelings are normal and can often be used to bring about positive changes you want to make in your life.
If the feelings of depression don't lift after a week or two, are impacting your functioning, or if making changes in your life seems overwhelming, seek help from your doctor or a drug counselor. As with other mood changes, depression can be substance-induced or pre-existing to your cannabis use, and it is treatable.
If you or a loved one are struggling with depression and addiction, contact the Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline at 1-800-662-4357 for information on support and treatment facilities in your area.
For more mental health resources, see our National Helpline Database.
An estimated 46.9% of former pot smokers report sleep disruption problems, including insomnia (trouble getting to sleep or staying asleep), unusually vivid or disturbing dreams, and night sweats during cannabis withdrawal.
Others who have quit smoking report having "using dreams" in which they dream they smoke marijuana. Frequent, vivid dreams typically begin about a week after quitting and can last for about a month before tapering off. Although some former users have reported having these types of dreams years after they stopped smoking pot.
Insomnia symptoms after you stop using weed can last a few days or a couple of weeks. Some people find that they can experience occasional sleeplessness for a few months after quitting.
Not everyone who stops smoking marijuana experiences headaches, but for those who do, the headaches can be very intense, especially during the first few days after quitting.
Headaches, like most other symptoms of withdrawing from marijuana use, will usually begin one to three days after quitting and will peak two to six days after stopping. Symptoms usually fade after two weeks, but some former smokers report continued symptoms for several weeks or even months later.
Other Physical Symptoms
Physical symptoms of marijuana withdrawal tend to be less intense, peak sooner, and fade more quickly than the psychological symptoms associated with quitting. The frequency and amount of marijuana used prior to stopping affect the severity and length of the withdrawals, which may include:
- Stomach pain
- Changes in appetite
- Weight loss or gain
- Flu-like symptoms, such as headache, sweating, shakiness and tremors, fever and chills
Coping & Relief
Making a few healthy lifestyle changes and employing some coping strategies can help you get through this period of withdrawal:
- Stay physically active to help ease bodily tension.
- Let friends and family members know when you need support or space.
- Avoid situations that you find anxiety-provoking, such as loud, crowded parties.
- Practice relaxation techniques, such as meditation.
- Establish sleep rituals and avoid caffeine too close to bedtime.
There are no worrisome dangers in quitting marijuana cold-turkey or detoxing on your own. That said, consulting a medical professional can help you better manage the physical and psychological symptoms of withdrawal and prevent relapse.
Just as people with alcohol use disorder who are trying to quit drinking may pick up a drink to relieve the symptoms of alcohol withdrawal, marijuana users may be tempted to light up a joint to relieve the discomfort they experience when they try to stop smoking pot.
One study found that 70.4% of users trying to quit smoking marijuana relapsed to relieve the withdrawal symptoms.
In many cases, the symptoms of weed withdrawal will dissipate with time and can be treated without medical attention. However, if your symptoms last for more than a couple of weeks, you should see your doctor or mental health professional.
Make sure you tell your doctor that marijuana withdrawal is playing a role in how you are feeling. If you just say you are depressed or anxious, you may be prescribed medication, like benzodiazepines, that can present its own set of dependence issues.
Fortunately, many non-addictive pharmacologic options exist for anxiety, as well as non-drug treatments, such as cognitive-behavioral therapy (CBT).
If you have decided to quit smoking weed after regular use, chances are you will experience some kind of withdrawal symptoms. Depending on how much and how often you have been smoking, these symptoms could become intense enough to drive you to relapse to find relief.
But you don’t have to do it on your own. Seek help from your healthcare provider to deal with the physical symptoms of withdrawal or seek help from a support group like Marijuana Anonymous to handle the psychological symptoms.
A Word From Verywell
Experiencing the symptoms of cannabis withdrawal can be unpleasant and may temporarily interfere with performance at work, school, and daily life. While withdrawing from marijuana use can present challenges, remember that what you are going through will pass. Be patient. Making life changes is always challenging, but with the right support, they can be transformative.