Cannabis and Pregnancy UK: Risks, Evidence and Medical Advice

Current UK Guidance on Cannabis Use During Pregnancy

The UK’s medical regulatory bodies, including the Royal College of Obstetricians and Gynaecologists (RCOG) and the National Institute for Health and Care Excellence (NICE), recommend that cannabis should be avoided during pregnancy. This guidance applies to both recreational and medical use. The RCOG states that evidence suggests cannabis use in pregnancy may be associated with adverse pregnancy and child health outcomes, though the committee acknowledges that further research is needed in some areas.

The UKCA (UK Competent Authority) and General Medical Council advise healthcare professionals to counsel women of childbearing age about the risks of cannabis use if they are planning pregnancy or are already pregnant. However, UK guidance also emphasises that pregnant women should not be judged or penalised for disclosing use; instead, they should receive support and evidence-based care.

Evidence of Risks to Foetal Development: Low Birth Weight and Preterm Birth

Research published in peer-reviewed journals indicates that maternal cannabis use during pregnancy is associated with several adverse outcomes. Multiple systematic reviews have found associations between prenatal cannabis exposure and reduced birth weight, with some studies suggesting a reduction of approximately 100-200 grams on average compared to unexposed pregnancies.

Preterm birth (delivery before 37 weeks) has also been linked to cannabis use in pregnancy in several observational studies. However, researchers note that determining causation is complex, as women who use cannabis may have other risk factors that independently increase preterm birth risk, such as smoking cigarettes or socioeconomic factors.

The active ingredient THC (tetrahydrocannabinol) crosses the placental barrier and can accumulate in foetal tissue. Animal studies suggest THC may affect neurodevelopment, though direct evidence in human pregnancies is limited. Long-term neurodevelopmental effects in children exposed prenatally to cannabis remain an area requiring further research, with some studies suggesting potential impacts on attention and executive function, though causality is not definitively established.

CBD During Pregnancy: Is It Safe?

Cannabidiol (CBD) is often marketed as a safer cannabis alternative, but evidence specifically examining CBD use in human pregnancy is extremely limited. The RCOG has not identified CBD as demonstrably safe during pregnancy. Most pregnancy-related cannabis guidance does not differentiate between CBD and THC-containing products, recommending caution with all cannabis-derived compounds.

One key concern is that CBD products, particularly those from unregulated sources, may contain variable amounts of THC or other contaminants. Additionally, CBD can interact with medications commonly used in pregnancy and may affect liver enzymes involved in drug metabolism. Until rigorous human studies are conducted, CBD cannot be recommended as safe during pregnancy.

If you are considering medical cannabis or CBD products, discussion with your obstetrician or midwife is essential before pregnancy or immediately upon discovering pregnancy.

Medical Cannabis Prescriptions During Pregnancy: Can You Continue?

Under the UK cannabis law, medical cannabis can be prescribed by specialist doctors for certain conditions, including chronic pain and epilepsy. However, if a woman holding a medical cannabis prescription discovers she is pregnant, guidance recommends discussing this with her prescribing specialist and obstetric team immediately.

In most cases, medical cannabis prescriptions are not continued during pregnancy. Instead, healthcare providers will work with the patient to identify alternative treatments with better safety profiles in pregnancy. For example, women with chronic pain may transition to physiotherapy, pregnancy-safe analgesics like paracetamol or certain NSAIDs, or other evidence-based approaches.

The decision to discontinue medical cannabis should involve shared decision-making between the woman, her prescribing doctor, and her obstetric team. Abrupt cessation should be avoided; instead, a managed tapering plan should be established. Women should never discontinue prescribed medications without medical guidance, as this can also pose risks.

Morning Sickness and Cannabis: Evidence Review

Some women consider using cannabis to manage pregnancy-related nausea and vomiting (hyperemesis gravidarum). However, evidence does not support cannabis as a treatment for morning sickness in pregnancy. The RCOG does not recommend cannabis for this indication, and no randomised controlled trials have examined its safety or efficacy in pregnant populations.

Evidence-based treatments for pregnancy-related nausea include vitamin B6, ginger (in appropriate doses), and antiemetic medications such as ondansetron or metoclopramide, which have been studied in pregnancy. These should be discussed with your healthcare provider.

What Happens if You Disclose Cannabis Use to NHS Midwives?

Many pregnant women worry about consequences of disclosing drug use to NHS staff. It is important to know that disclosing cannabis use to midwives and doctors does not automatically trigger involvement of child protection services. The NHS approach is non-judgmental and focused on providing support and evidence-based care.

Healthcare professionals are trained to engage women without stigma. Disclosure allows them to provide appropriate monitoring, discuss risks honestly, and offer alternatives. If you use cannabis, informing your midwife enables proper antenatal care and allows discussions about cessation support if appropriate.

Only in cases where there are concerns about significant harm or child safeguarding will other agencies become involved. Most cannabis use alone, without additional risks, does not trigger safeguarding referrals in pregnancy.

Breastfeeding and Cannabis

THC is lipid-soluble and concentrates in breast milk. Research indicates that THC in breast milk exposes infants to the compound. Effects on infant neurodevelopment have not been comprehensively studied, but the RCOG recommends avoiding cannabis during breastfeeding as a precaution.

If you used cannabis during pregnancy and plan to breastfeed, stopping use before breastfeeding begins is advisable. If you wish to continue using cannabis and cannot stop, discussion with your healthcare provider about feeding options is necessary.

If You Were Using Cannabis Before Discovering Pregnancy

Learning you are pregnant after using cannabis can provoke anxiety. However, early pregnancy exposure is unlikely to cause significant harm. The critical period for foetal development occurs across the entire pregnancy, not solely in early weeks. The most important action is to stop using cannabis now and discuss your use with your midwife or doctor, who can provide reassurance, monitor your pregnancy appropriately, and support cessation if you wish to continue.

Safer Alternatives for Pain and Anxiety in Pregnancy

Evidence-based alternatives to cannabis for pain management in pregnancy include paracetamol, physiotherapy, acupuncture, and pregnancy-appropriate exercise. For anxiety, cognitive behavioural therapy, mindfulness, and certain antidepressants (like sertraline) have safety data in pregnancy.

Your healthcare provider can discuss which options are appropriate for your specific condition and medical history.

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