Cannabis is the most commonly used federally illegal drug, with its acceptance growing in recent years due to increased legalization and availability.
In the movement to legalize cannabis, there has been a concerted effort made to emphasize its potential medicinal properties and therapeutic uses.
Here are some of the clinically established benefits that may be associated with cannabis use:
Can act as an antiemetic, reducing nausea and vomiting in chemotherapy patients.
May reduce pain symptoms in those suffering from chronic pain.
Can improve neuropathic pain, disturbed sleep and spasticity symptoms in patients with Multiple Sclerosis (MS).
Can lower intraocular pressure caused by glaucoma.
Has been found to improve appetite, weight gain, mood and quality of life among patients with AIDS.
Cannabinoids, such as THC and CBD, exhibit anti-inflammatory effects and may be beneficial in the treatment of inflammatory conditions, including rheumatoid arthritis, ulcerative colitis and Crohn’s disease. Cannabis with a high cannabidiol content has been effectively used to treat epileptic seizures in children.
Further study into the medicinal uses and therapeutic effects of cannabis and cannabinoids is likely to occur as acceptance and legalization continues to grow.
It’s important to note that the potency of THC––the active component in cannabis––has also increased over time, with substantial increases in THC levels seen particularly in the last decade.
This means cannabis and its biochemical physiological effects are now stronger than ever before. As widespread acceptance, use and potency of cannabis increases, it’s worth exploring the potential adverse effects cannabis may have on human health.
Adversely Affects Male Fertility
The negative influence of cannabis on male fertility primarily impacts sperm quality and sperm quantity. Heavy users of cannabis tend to have lower sperm count and lower sperm concentrations, as well as adverse changes to sperm morphology and sperm motility.
Additionally, sperm viability (the percentage of live sperm found in a semen sample) and sperm capacitation (the changes sperm must undergo to be able to penetrate and fertilize an egg) are adversely affected by cannabis use.
While cannabis can increase short-term libido, the long-term effects of regular cannabis use can lead to gynecomastia (“man boobs”), erectile disorders and diminished erectile function.
Lowers Sperm Count
One study evaluating 1,215 Danish men aged 18-28 between 2008 and 2012 found a 28% lower sperm concentration and a 29% lower total sperm count in those who smoked cannabis more than once per week.
The combination of cannabis use more than once per week and other recreational drugs lowered sperm concentration by 52% and total sperm count by 55%.
Cannabis use can also make it harder for sperm to fertilize an egg. Activation of the CB1 receptor by cannabis use not only decreases sperm motility and sperm viability, it also inhibits the acrosomal reaction, which is the reaction that takes place during the fertilization of an egg by sperm, wherein the sperm fuses to and penetrates the outer membrane of the egg.
Additionally, activation of CB2 receptors by cannabis use can make sperm slower and more sluggish, as it appears endocannabinoids may interfere with sperm mitochondrial activity. Mitochondria are central to energy production in cells, including sperm.
Testicular Cell Death
Cannabis use can also contribute to the death of Sertoli cells, which are testicular cells essential to the formation of healthy sperm. The higher the endocannabinoid levels are in semen, the worse the sperm motility and sperm production will be, and thus the greater the reduction in overall male fertility.
Cannabis use can even alter the epigenome of sperm, leading to the potential for passing down undesirable inherited changes in gene expression to the male’s children.
Adversely Affects Reproductive Health
Cannabis has been found to have adverse effects on both male and female reproductive health.
Cannabinoid receptors have been identified in the ovaries, endometrium, testes, sperm, the placenta and more, indicating the endocannabinoid system can influence the reproductive processes of both men and women.
Effects In Men & Women
In men, cannabis has been associated with erectile dysfunction, abnormal spermatogenesis and testicular atrophy.
In women, cannabis can have an adverse impact at every level of reproductive health, from preconception to pregnancy, during lactation and throughout menopause.
Association With Female Infertility
There is substantial evidence that cannabis use can disrupt ovulation, tubal transportation, and embryo implantation and development, contributing to infertility in women.
A 2019 study looking at the role of the endocannabinoid system in female reproductive tissues concluded that cannabinoids from cannabis use may disrupt the natural balance of a woman’s innate endocannabinoid system, leading to infertility by dysregulating ovarian function.
Impairs In Vitro Fertilization
A study involving women undergoing in vitro fertilization found that current cannabis users had more than double the likelihood of pregnancy loss after their fertility treatment: 54% of cannabis users lost their pregnancy, while only 26% of past or non-cannabis users lost their pregnancy.
Adversely Affects Offspring
Delta-9-tetrahydrocannabinol (THC)––the primary psychoactive component of cannabis––can cross the placenta and has been found in breast milk up to six days after cannabis use. Animal studies have shown chronic cannabis exposure can delay sexual maturation.
Impact On Pregnancy & Lactation
Cannabis use during pregnancy and/or lactation is associated with lower birth weight, lower body length and head circumference, increased preterm birth, poor fetal neurodevelopment, more frequent need for neonatal intensive care, underdeveloped infants, and impaired social behavior and cognitive development in offspring, including an increased risk of autism spectrum disorder, intellectual disability, learning disorders and sleep disorders.
Link To Childhood Leukemia
Prenatal cannabis exposure has been linked to elevated rates of childhood leukemia, which is a broad term for cancers of the blood cells. Acute lymphoid leukemia (ALL) is the most common childhood cancer and is on the rise in many countries. Studies show ALL is associated with cannabis use and that increased acceptance of cannabis may exacerbate incidences of ALL.
Link To Childhood Cancers
Besides leukemia, childhood cancers in general have been found to be linked to cannabis use, and rates of childhood cancers are higher in cannabis-liberal areas. A 2021 epidemiological study evaluated available data from a CDC cancer database, the Drug Enforcement Agency, a National Survey of Drug Use and Health and the US Census.
In confirming the close link between cannabis and total pediatric cancer incidence rates in the US––which have risen 49% between 1975 and 2015––study authors cited prenatal cannabis exposure and cannabinoid-induced genotoxicity as the cause.
Promotes Addictive Behavior
Beyond childhood, exposure to cannabis in utero can lead to a higher propensity for addictions later in life. This is due to in utero cannabis exposure decreasing dopamine receptor 2 mRNA in the nucleus accumbens of the brain, which influences rewarding behaviors by releasing dopamine, including feeding, sex, and self-adminstration of drugs.
Adversely Affects Hormonal Balance
Cannabinoids in cannabis affect the hypothalamic–pituitary–gonadal (HPG) axis, which is central to the production of sperm and sex hormones, such as testosterone, estrogen and progesterone.
In women, the HPG axis is involved in the regulation of the menstrual and ovarian cycle. In men, the HPG axis is involved in the production of testosterone and the process of spermatogenesis.
Alters Hormone Production
Chronic exposure to cannabis can decrease gonadotropin-releasing hormone (GnRH) in a dose-dependent manner, meaning the more cannabis one consumes, the more GnRH decreases.
GnRH stimulates the pituitary gland to make luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
In men, these hormones stimulate the testicles to produce testosterone. In women, they stimulate the ovaries to produce estrogen and progesterone.
So, cannabis use can directly affect the production of testosterone levels in men and estrogen and progesterone levels in women.
Disrupts Hormonal Balance
THC can depress prolactin, thyroid gland function, and growth hormone while elevating adrenal cortical steroids. Decreased prolactin levels in women may result in menstrual cycle disruptions.
THC can cross the blood-testis barrier and causes a dose-dependent reduction in testosterone levels and sperm concentration, meaning the more THC is consumed, the more testosterone and sperm concentration decrease.
Association With Cancer
Potential Anti-Cancer Effects
Overall, there is preliminary evidence supporting cannabis as having a generally anti-cancer effect. Cannabinoids may be able to stop cancer cells from growing and dividing, as well as lead to cancer cell death and prevent spread to other tissues. However, these findings are primarily based on pre-clinical, laboratory and animal studies—human cells often behave very differently than lab and animal cells.
Links To Reproductive Cancer
Conversely, there also exists evidence in human study that cannabis use is associated with an increased risk for some site-specific cancers, including prostate cancer, ovarian cancer, cervical cancer and testicular cancer.
A California study from 1997 examining the relationship between cannabis and cancer in 64,855 patients found that cannabis use was associated with an increased risk for prostate and cervical cancers. A 2022 epidemiological study of the US found that cannabidiol was associated with prostate and ovarian cancers.
Increased Risk For Testicular Cancer
Heavy cannabis use––defined as more than 50 times in a lifetime––was associated with a 2.5-fold increased risk of testicular cancer according to a study that observed Swedish men over a 42 year timespan.
Another study found that cannabis use is associated with the development of testicular germ cell tumor (TGCT) and that cannabis accelerates the pathway to developing this type of testicular cancer by several decades.
The same study found states with liberal cannabis legislation had higher rates of testicular cancer, with study authors asserting increased cannabis acceptance and use as the cause.
THC and other related cannabinoids appear to demonstrate a strong genotoxic dose-response effect, meaning the more cannabis one uses, the greater the likelihood of developing testicular cancer.
Disrupts Cancer Treatment
For those receiving cancer treatment, cannabis use may adversely impact conventional treatment of some cancers by decreasing effectiveness and increasing toxicity of the cancer treatment itself.
This is due to the inhibitory interaction cannabis has with cytochrome P450 enzymes, which are necessary for the detoxification of foreign chemicals and the metabolism of drugs.
In an Israeli study that looked at the impact of cannabis use during drug immunotherapy treatment for cancer, treatment was found to be 37.5% less effective in those who used cannabis, compared to 15.9% in those who did not use cannabis.
Cannabis users in this study experienced 39% overall benefit from their immunotherapy drug treatment, while non-cannabis users experienced a higher overall benefit at 59%. The average time to tumor progression (when a tumor becomes more aggressive and malignant) was nearly four times faster in cannabis users at 3.4 months versus non-cannabis users at 13.1 months.
Smoke May Be Carcinogenic
There are many studies that supply strong evidence inhaled cannabis smoke is carcinogenic on a cellular and molecular level, however, the epidemiologic evidence is still inconclusive.
Presently, there is evidence both for and against the role of cannabis in prevention and treatment of cancer. Research has been limited over the years due to cannabis' classification as a schedule I substance. However, as cannabis continues to become legalized, more research should be conducted to further investigate its effects on cancer in humans.
Association With Mental Disorders
Cannabis increases the risk of developing mental disorders, including schizophrenia, social anxiety disorder and other psychoses. The more cannabis one consumes, the greater the risk becomes.
Bipolar symptoms can become exacerbated by regular cannabis use in those diagnosed as bipolar, and some cases of depression are worsened with cannabis.
Heavy cannabis use is also associated with increased reported thoughts of suicide.
Impairs Cognition & Academic Performance
Cannabis can impair cognitive performance, learning, memory and attention.
Cannabis use during adolescence can also impair academic achievement, education, employment, income, social relationships and social roles.
Studies show that adolescents who use cannabis are significantly less likely to finish high school or obtain a degree compared to peers who do not use cannabis.
Cannabinoid Hyperemesis Syndrome (CHS)
Cannabinoid hyperemesis syndrome (CHS), which was first described in Australia in 2004, is characterized by cyclical nausea, vomiting, and abdominal pain due to chronic use of cannabis.
While CHS can often be relieved by hot showers, the only way to indefinitely resolve CHS symptoms is with the complete cessation of cannabis. After stopping the use of cannabis, it can take up to a few weeks for CHS symptoms to fully abate.
Various agents have been used to treat CHS symptoms, including dopamine antagonists, antihistamines, serotonin antagonists, antipsychotics, and topical capsaicin.
Continuing to use cannabis with CHS can potentially lead to life threatening complications.
Benefits & Adverse Effects
While cannabis has been found to possess various therapeutic effects and medicinal properties, it has also been found to have many adverse effects, particularly on reproductive health, hormonal balance, offspring development, cancer, mood disorders, cognition and more.
More Research Required
As we move into an age of decriminalized and legalized cannabis––a change that is necessary and long-overdue––it’s important that we pursue thorough and in-depth clinical research into the evaluation of all aspects of cannabis' potential impacts on human health, both good and bad.
In this way, each individual can make a clear and informed decision as to whether the use of cannabis in their life might be beneficial or not.