Cannabis & fertility: facts for couples trying to conceive

TL;DR

• Sperm: -28 % concentration, motility ↓ with regular use (Payne 2019 meta-analysis).
• Women: longer follicular phase, reduced progesterone peak – ovulation can shift.
• IVF: lower fertilisation rates in THC-positive men.
• Effects largely reversible after 3-6 months of abstinence.

The endocannabinoid system in reproduction

CB1 receptors sit in testes, epididymis, fallopian tubes and uterus. Exogenous THC over-stimulates the system, shifts the hormonal axis and disturbs sperm maturation. In women it affects follicle selection and implantation.

Recommendation when trying to conceive

Both partners should abstain from cannabis for at least 3 months pre-conception. For IVF, ≥ 6 months is preferable.

Hormonal regulation under the influence of THC

The control of human reproduction is subject to the hormonal regulation of the hypothalamic-pituitary-gonadal axis. Exogenous cannabinoid intake directly interferes with this feedback loop by disrupting the pulsatile release of gonadotropin-releasing hormone in the hypothalamus. Consequently, the secretion of luteinising hormone and follicle-stimulating hormone from the pituitary gland decreases. In men, this leads to reduced testosterone production in the testes, which impairs sperm maturation. In women, the absence of the hormonal peak can delay or completely prevent ovulation, thereby extending the time to potential fertilisation.

In addition to classical sex hormones, the endocannabinoid system also influences prolactin release and the body's own stress axis. A permanently elevated cannabinoid level can cause an increase in prolactin in the blood, which further dampens ovarian function. These complex interactions illustrate that the impairment of fertility does not only occur at a local level in the reproductive organs, but is primarily caused by a malfunction in the brain. After cessation of consumption, the endocrine system requires several weeks to fully re-establish natural hormonal pulsatility.

• Disruption of the pulsatile release of gonadotropin-releasing hormones in the brain
• Reduced secretion of the hormones LH and FSH, which are essential for germ cell maturation
• Impaired testosterone synthesis in the Leydig cells of the testes
• Possible increase in prolactin levels with negative effects on the female cycle

Swiss advisory practice and regulatory aspects

In Switzerland, the topic of family planning and substance use is increasingly addressed during medical consultations as well as within the scientifically monitored pilot trials such as Züri Can or Weed Care. The Federal Office of Public Health and the Federal Commission for Issues relating to Addiction and Prevention point out the risks of cannabis in the preconception phase in their guidelines. Since medical cannabis can be prescribed directly by doctors without an exceptional licence from the FOPH since August 2022, Swiss gynaecologists and reproductive medicine specialists are increasingly required to actively advise patients wishing to have children on the risks of continuing the therapy.

The legal regulation under which cannabis products with a total THC content of less than one per cent are not subject to the Narcotics Act often leads to an underestimation of the risks in practice. Even though such products are legally available on the market, Swiss experts recommend strict abstinence when trying to conceive, as sound safety data is lacking. For questions regarding accidental exposure in early pregnancy, Tox Info Suisse provides initial medical guidance via the emergency number 145. Swiss fertility centres standardly integrate the assessment of consumption habits into their evaluations to minimise risks at an early stage.

• Addressing consumption within the framework of the state-approved Swiss pilot trials
• Medical duty to inform when prescribing medical cannabis since August 2022
• Precautionary principle also applies to CBD products below the legal limit of one percent THC
• Tox Info Suisse (telephone 145) as an established point of contact in the event of unforeseen exposure

Implantation and early embryonic development

The importance of the endocannabinoid system extends far beyond fertilisation alone and is of critical relevance for the first days of pregnancy. After conception, the fertilised egg must be transported through the fallopian tube into the uterus. This transport is significantly controlled by the coordinated activity of CB1 receptors. Overstimulation of these receptors by exogenous THC can slow down fallopian tube contractions and ciliary beat. This increases the risk of the embryo implanting in the fallopian tube, which can lead to a life-threatening ectopic pregnancy.

In the uterus itself, precise regulation of the local cannabinoid concentration is required for successful implantation in the endometrium. Excessively high levels disrupt the decidualisation of the uterine lining, which is responsible for supplying the early embryo. Impaired implantation can lead to a very early pregnancy loss, which is often clinically perceived only as a delayed or particularly heavy menstrual period. Couples with fertility problems should be aware of this risk and safeguard the implantation phase by stopping consumption in good time.

• Influence on the timely transport of the embryo through the fallopian tube
• Increased risk of extrauterine pregnancies in the event of disrupted transport
• Impairment of the decidualisation of the uterine lining
• Risk of unnoticed, early pregnancy loss due to implantation failure

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