Effects on Nausea

  • Protective Mechanisms: Both nausea and vomiting are natural responses that have been refined through the process of evolution. Their primary purpose is to protect the organism from harmful substances. This means that when our bodies detect something potentially dangerous, like food that has spoiled or a toxic chemical, they trigger these responses to help eliminate the threat.

  • Detection and Expulsion: Nausea serves as a warning signal that lets us know we may have ingested something harmful. The experience of nausea prompts the body to vomit, which helps to expel these toxins before they can be absorbed into the bloodstream and cause more significant harm. Think of it as the body’s first line of defense against poisons.

  • Knowledge Gap: While science has made significant strides in understanding what causes vomiting (known scientifically as emesis) and how to treat it, there is still limited knowledge about what triggers nausea itself. This lack of understanding presents a gap in medical knowledge that researchers are working to fill.

  • Subjective Experience: People often find nausea to be extremely unpleasant. Studies show that when people rate various sensations on a scale from pleasant to unpleasant, nausea is frequently regarded as the most unpleasant feeling. This indicates just how distressing nausea can be, often described in a way that suggests it is more uncomfortable than physical pain.

  • Impact on Quality of Life: Unlike pain, which is often manageable with medication, nausea is often viewed as completely debilitating. Many people describe it as “crippling”, meaning it can be so severe that it prevents them from doing everyday activities. This highlights the significant impact nausea can have on someone’s life, possibly disrupting their daily routines and activities due to the overwhelming discomfort.

Modern Medical History and Chemotherapy

  • Early Regulatory Use: The early 1980s marked the first application of a chemical called THC (Tetrahydrocannabinol) in modern Western medicine. This compound, found in cannabis, was specifically approved to help manage the nausea and vomiting experienced by patients undergoing chemotherapy for cancer treatment. Chemotherapy often comes with severe side effects, and THC was looked at as a beneficial treatment.

  • Efficacy vs. Standard Care: In clinical settings, THC has been found to be roughly as effective as modern antiemetics (medications that prevent vomiting), especially those that block serotonin (a chemical in the brain). This discovery has made THC a significant option for patients who struggle with nausea due to cancer treatments.

  • Role of Serotonin: Serotonin is a neurotransmitter that plays a crucial role in triggering the vomiting response. In medical treatments, one common strategy is to block the action of serotonin to prevent nausea and vomiting. This is how both THC and traditional antiemetics operate in helping patients.

Classification of Vomiting and Nausea

  • Acute Vomiting: This refers to the immediate vomiting that occurs right after ingesting something toxic or poisonous. It is a rapid response aimed at quickly removing harmful substances from the stomach.

  • Delayed Vomiting: Unlike acute vomiting, delayed vomiting happens after a certain period. For example, if someone eats spoiled sushi, they might not feel sick right away, but hours later, they could feel ill and vomit. This type of vomiting can occur in chemotherapy patients days after they receive their treatment due to the effects of the medication.

  • Anticipatory Vomiting/Nausea: This involves learned responses, where the body prepares to vomit due to past experiences.

    • Chemotherapy Context: Patients undergoing chemotherapy might start feeling nauseated or even vomit when they enter a hospital for more treatment, even before they receive the medication. The mere anticipation of the treatment can trigger these unpleasant sensations.

    • Anecdotal Example (Empanada Story): A speaker narrated a personal story about eating empanadas at a gas station restaurant in Costa Rica and subsequently falling ill. This negative experience led to a condition called anticipatory nausea, where the sight of empanadas now triggers feelings of nausea from the memory of that experience.

  • THC Treatment: THC has been shown to effectively block acute, delayed, and anticipatory vomiting. Remarkably, it only requires a relatively low dose to achieve its antiemetic effects, which is often below the threshold needed to cause psychoactive effects (the feeling of being 'high').

Animal Models and the Discovery of "Gaping"

  • The Rodent Dilemma: Mice and rats cannot vomit due to their anatomical structure, which makes them poor models for studying emesis in laboratory conditions. This poses a challenge for researchers trying to understand vomiting mechanisms.

  • Alternative Research Models: Scientists have turned to animals like ferrets and shrews, as they possess the physical ability to vomit, making them better subjects for studies focusing on this response.

  • The Role of the CB1 Receptor:

    • Research in ferrets and shrews indicates that THC can reduce vomiting. When a CB1 antagonist (a compound that blocks the action of the CB1 receptor) is given alongside THC, the anti-vomiting effect is negated, showing that the mechanism of THC involves the CB1 receptor.

    • Interestingly, administering a CB1 reverse agonist alone can induce spontaneous vomiting, suggesting that the CB1 receptor plays a role in keeping vomiting at bay.

  • Measuring Nausea through "Gaping": Since animals cannot verbally express their feelings of nausea, scientists have sought behavioral indicators to gauge nausea levels.

    • In rodents, researchers observed a behavior called "gaping," where they open their mouths wide, mimicking the act of vomiting but without actually expelling anything. This behavior has become a recognized way to objectively measure nausea in rats.

    • Current treatments for nausea in humans do not block anticipatory gaping in rats, but CB1 agonists like THC have shown the ability to prevent this behavior, suggesting their potential to treat nausea effectively in humans.

Cannabis Side Effects: Hyperemesis

  • Cannabinoid Hyperemesis Syndrome: Paradoxically, while cannabis can be effective in treating nausea in some contexts, chronic use of cannabis can lead to a condition known as hyperemesis, where individuals experience uncontrollable and repetitive vomiting.

  • Comparison to Pregnancy: This syndrome is akin to hyperemesis gravidarum, a severe form of nausea and vomiting that some women encounter during pregnancy, which can severely affect quality of life.

  • Downregulation Hypothesis: A proposed reason for the occurrence of hyperemesis is that long-term exposure to cannabis leads to downregulation (a decrease in receptors) of the CB1 receptor. This reduces the overall signaling of endocannabinoids (the body’s natural cannabinoids), mimicking the action of a CB1 reverse agonist and promoting spontaneous vomiting.

Comparative Cannabinoid Pharmacodynamics

  • CBD (Cannabidiol):

    • Biphasic Effect: In animals such as shrews, low doses of CBD have been found to decrease vomiting, while high doses can actually increase it. This indicates that the effects of CBD can vary based on dosage.

    • Scope: Low-dose CBD appears to be effective in preventing both acute and anticipatory nausea, although delayed nausea treatments are less understood.

    • Mechanism: One theory is that CBD works by inhibiting the release of serotonin, which is known to play a role in inducing nausea.

    • THC Synergy: Interestingly, THC and CBD work together to improve the effectiveness of anti-nausea treatments, despite CBD typically acting as a negative allosteric modulator that can antagonize THC in other contexts. This synergy may enhance their combined antiemetic effects.

  • Acid Precursors (THCA and CBDA): These are the raw forms of THC and CBD found in the cannabis plant before they undergo a heating process to become active compounds.

    • THCA (THC Acid): THCA is believed to be about ten times more potent than THC in preventing nausea and vomiting.

    • CBDA (CBD Acid): CBDA is estimated to be between 100 to 1000 times more potent than CBD, indicating its potential for therapeutic applications.

    • Synergistic Potential: CBDA may work well with existing medications that block serotonin, suggesting possibilities for improved combined therapies to manage nausea.

  • Minor Cannabinoids: Other cannabinoids such as THCV and CBDV have shown promise in reducing nausea, but they are less researched than THC and CBD.

  • CBG: Cannabigerol (CBG) is another cannabinoid that can inhibit the anti-nausea effects of CBD, highlighting the complex interactions among cannabinoids in regards to nausea treatment.

Endocannabinoid Regulation and Motion Sickness

  • General Anesthesia: After undergoing general anesthesia, many patients experience nausea frequently. Research indicates that individuals suffering from post-operative nausea have significantly lower levels of a cannabinoid known as AEA (Anandamide) in their systems.

  • Motion Sickness:

    • Individuals who experience motion sickness have measurable drops in AEA levels during such episodes, whereas those who do not suffer from motion sickness maintain stable AEA levels. This suggests a link between the endocannabinoid system and the experience of nausea related to motion.

  • Enzyme Inhibitors: Certain compounds can inhibit enzymes like FAH and MAGL, which break down endocannabinoids. Veterinary studies suggest that these inhibitors can raise internal cannabinoid levels. In turn, increased endocannabinoid levels have been observed to block both acute and anticipatory nausea in animal studies.

The Neurological Pathway and Negative Feedback Loop

  • GI Tract Signal: The signals that induce nausea and vomiting originate from the gastrointestinal (GI) tract, particularly when toxins or harmful substances are detected.

  • Brainstem Relay: These signals then travel to the brainstem, specifically passing through areas known as the Area Postrema and the Parabrachial Nuclei, which are key regions for processing nauseaS and vomiting impulses.

  • Forebrain Processing: From the brainstem, the signals are forwarded to the Interoceptive Insular Cortex in the forebrain, which processes the experience of nausea.

  • Chemical Cascade:

    • This signaling pathway leads to an increase in the release of serotonin, which contributes to the sensation of nausea in the body.

    • Additionally, as a response, the body elevates levels of the endocannabinoid 2-AG, which plays a crucial role in regulating and reducing nausea sensations.

  • Negative Feedback Loop: The rise in 2-AG helps to combat the feeling of nausea and vomiting, acting as a natural mechanism to prevent the response from lasting too long or escalating beyond control, thereby maintaining balance in the body’s response to perceived threats.