Cannabidiol (CBD) health benefits and products are still dominating the news since the cannabis compound was decriminalized late last year in the U.S. It is now legal for use in most states, even though its lawful regulation is still in a tangle. Also, it is old news that when taking a small amount of the other cannabinoid, tetrahydrocannabinol (THC), together with CBD, nausea and vomiting can be managed successfully in a number of conditions. This includes nausea associated with chemotherapy for cancer. Many doctors are recommending (not prescribing) it, because while much more clinical research is needed, it is generally considered safe for use in humans in low to medium doses.  
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Before we take a look at how THC, CBD, nausea, and vomiting are linked, it’s important to note that CBD is not registered as a medicine for any use other than in retractable epilepsy. This landmark ruling by the U.S. Food and Drug Administration (FDA) also took place last year, particularly for the treatment of Dravet and Lennox-Gastaut syndromes. It’s a very strong cannabidiol medicine that can only be obtained via prescription. Any CBD health product claiming to be good for medicinal use is advertising this illegally and should be avoided.
THC, CBD, Nausea, and Vomiting—Background
When taking only CBD, nausea and vomiting are not known to disappear readily. It works together with THC, as mentioned, in what is often referred to as the “entourage effect.” This basically means that the different cannabis compounds seem to work better together, as opposed to when taken on their own. 
Chemotherapy-related nausea is further complicated by the so-called “nocebo effect,” which consists of negative expectations of treatment that lead to cancer patients anticipating nausea.
THC as such, found abundantly in marijuana, is still outlawed federally and in many states. This is the cannabinoid known to cause the typical “high” weed is popularly used for. Fortunately, the small amount of THC found in hemp (the decriminalized form of cannabis) is unlikely to get anyone in trouble with the law. Also, THC is under investigation for a myriad of health properties of its own, even though the cannabinoid’s somewhat notorious psychotropic ability limits its medicinal study and use.
But to return to the pair of cannabinoids’ effects on nausea and vomiting—studies seem to be generally unanimous that they work well to curb these symptoms. More about that further on, though, because anecdotal evidence is also encouraging.
In an article for Project CBD, Stacey Kerr, M.D., writer, teacher, and qualified physician, reported recommending CBD for a friend and fellow doctor undergoing chemotherapy. Laura was a doctor herself who treated many patients for substance abuse, so she had a strong negative bias against cannabis use. When she was diagnosed with breast cancer, the nausea caused by the cancer therapy accompanied by anxiety was so debilitating that she was willing to try a vaporized form of CBD recommended by her friend. According to Kerr:
This is encouraging and is supported by scientific evidence, as reported in a 2010 review of the data:
“Recently, evidence from animal experiments suggests that cannabinoids may be especially useful in treating the more difficult-to-control symptoms of nausea and anticipatory nausea in chemotherapy patients, which are less well controlled by the currently available conventional pharmaceutical agents.” 
But how do THC and CBD for nausea work?
CBD For Nausea—How Does It Work?
While the exact mechanisms aren’t clear yet, the general consensus among researchers is that first of all:
- As mentioned, it seems to work to curb toxin- and anxiety-induced nausea and vomiting, especially in animal models in a variety of species, and
- that this is done via manipulation of the endocannabinoid system (ECS) with its multiple receptors.  
More specifically, an animal study concluded that CBD reduced the nausea and vomiting response by activating serotonin receptors in the brains of rats. 
Another one went further, suggesting that cannabinoids without psychoactive side effects—such as CBD—may have therapeutic value in the treatment of chemotherapy-induced nausea. 
THC, in turn, activates CB1 receptors in the brain, which is known to reduce vomiting. In her article, Kerr also speculates that THC’s mood-lifting properties could play a role in reducing anxiety-induced nausea if taken in small amounts. 
CBD is a known anxiolytic.
How Should CBD With THC Be Taken for Nausea?
Whatever causes nausea, start with a 2:1 CBD:THC ratio product, preferably in an oil, tincture, or vaporizer format. These can be taken sublingually—or inhaled in the case of a vaporizer—so it will be fast-acting. This way, the body absorbs the compounds very quickly.
When searching a good CBD product, always look for ethical sellers who operate above suspicion in terms of manufacturing, legal advertising, etc. The label would, first of all, clearly state the amount of whole-plant cannabinoid content, so you can see that it contains mainly CBD with only a little THC. There should also be a laboratory report readily available for scrutiny by the public.
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Since there is every indication that when taking THC and CBD, nausea and vomiting for many conditions can be addressed, it’s best to use a high-quality product. Always consult with a physician before replacing any prescribed medicine with a plant product.