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CBD & Hemp Extract Supplements, Lotions, and Balms Review
What is it? CBD (cannabidiol) is a compound derived from hemp and marketed as a supplement despite the U.S. FDA's position that CBD is not a dietary supplement.
Does it work? CBD taken orally has been shown to reduce the frequency of certain types of seizures, and preliminary evidence suggests it may also help with anxiety, schizophrenia, and other conditions. However, most of these effects have involved large doses of CBD — hundreds of milligrams per day, which is more than in many marketed CBD supplements and products. CBD applied to the skin (such as CBD creams, gels, and lotions) may modestly reduce some forms of pain (See What It Is and What It Does).
What did CL find? ConsumerLab found the dose of CBD per suggested serving ranged 15-fold from 1.3 mg to 22.3 mg, and the cost to obtain 10 mg of CBD from each product ranged over 5-fold from 80 cents to $4.54 (or $4.73 when including balms). Two products were discovered to contain less CBD than listed and one contained much more. (See What CL Found and use the Results table to compare the amounts of CBD and other cannabinoids in products).
What to look for? If you seek CBD, look for products that list the amount of CBD or cannabidiol per serving (and don't confuse that with the amount per entire bottle). If a product lists only "cannabinoids" it may contain some CBD but you won't know how much. Products may still have significant amounts of CBD if they list "hemp extract" as an ingredient, but don't expect much CBD if "hemp oil" is the only ingredient. (See ConsumerTips)
How much to take and when? Most of the research with CBD has involved high doses (several hundred milligrams daily). However, many CBD products on the market are lower dose and it is not clear if this dosing is effective. Nevertheless, to greatly increase CBD absorption, take it with or shortly after a fatty meal. (See ConsumerTips: Dosage)
Other concerns: High-dose CBD can cause a range of side effects (particularly gastrointestinal) and affect certain medications. For details, see Concerns and Cautions.
CBD Oil and Supplements with CL Founder, Dr. Tod Cooperman
What It Is:
Cannabidiol (CBD) and its precursor compound CBDa are dominant "cannabinoid" compounds found in hemp and cannabis (a hemp plant also known as marijuana). Unlike tetrahydrocannabinol (THC), which is another cannabinoid compound, CBD is not believed to be a psychoactive compound affecting perception and behavior.
What It Does: NOTE:The effects described below are primarily based on daily doses of hundreds of milligrams of CBD. Many CBD products on the market contain much lower amounts (providing tens of milligrams or less per day), and it is not known if these low doses are as effective as higher doses.
Epilepsy and seizure disorders
Much of the research with CBD has focused on the reduction of certain types of seizures. A placebo-controlled clinical trial found a high daily dose of CBD (20 mg per kg of body weight, i.e., hundreds of milligrams) to reduce the frequency of convulsions in a rare form of epilepsy known as Dravet syndrome in children and young adults, although it was also associated with a higher rate of adverse effects including diarrhea, vomiting, fatigue, pyrexia, somnolence, and abnormal results on liver-function tests (Devinsky, New Eng J Med 2017). Similarly, the same high daily dose reduced the number of drop seizures among people with treatment-resistant Lennox-Gastaut syndrome in a 3-month study. Seizures per month decreased 44% with CBD compared to 22% with placebo; however, again, those taking CBD also had a higher rate of adverse effects including diarrhea, somnolence, fever, decreased appetite, and vomiting (Thiele, Lancet 2018).
Both studies noted above were funded by GW Pharmaceuticals, the maker of the prescription oral solution of cannabidiol Epidiolex. It should be noted that after reviewing these studies, the United Kingdom's National Institute for Health and Care Excellence rejectedEpidiolex as a drug for treating these seizures in its draft guidance. The agency raised concerns about the trials, particularly their short duration, because other antileptic drugs are known to lose their effectiveness over time (Dijk, BMJ 2019).
A study in Nashville among 108 children with refractory epilepsy who had been treated with commercially marketed CBD preparations found that CBD could be as effective as the anticonvulsant drug clobazam when used as add-on therapy. A reduction in seizure activity of at least 50% occurred in 33%, 38%, and 44% of those who received, respectively, CBD, clobazam, and CBD+clobazam. Relative to clobazam, CBD seemed to increase alertness and increase verbal interactions. Sedation, which was common among those taking clobazam, did not occur among those taking only CBD. The average daily dose was about 3 mg of CBD per kilogram of body weight: e.g., 100 mg per day for a 73 lb child. (Porcari, Epilepsy & Behav 2018).
Parkinson's disease and movement disorders
CBD does not appear to improve motor symptoms of Parkinson's disease, such as tremor and difficulty initiating movement, or involuntary movements (dyskinesia) associated with the use of the anti-Parkinson's drug levodopa. However, CBD may be helpful for non-motor symptoms of Parkinson's disease, such as psychosis, mood and sleep disturbances — although more research is needed (Crippa, Eur Arch Psychiatry Clin Neurosci 2019).
For example, there have been some preliminary reports of CBD oil (150 mg to 400 mg) improving symptoms of psychosis, with no worsening of motor function, in individuals with Parkinson's disease and psychosis who were taking levodopa (Zuardi, J Psychopharmacol 2009). In three older men with Parkinson's disease and REM sleep behavior disorder (RBD) (characterized by intense dreams and behavior such as laughing, yelling, kicking and punching during sleep) who experienced disruptive sleep episodes between two and seven times per week, none experienced these symptoms during a six-week period of daily dosing with 75 mg of CBD. A fourth man, who took 300 mg of CBD daily for the same time period had a reduction in episodes from two to four times per week to once per week (Chagas, J Clin Pharm Ther 2014). A small, double-blind, placebo-controlled study in Brazil found no improvement in motor function in men and women with mild to moderate Parkinson's disease without other psychiatric conditions (average duration of disease 8 years) who took CBD oil (75 mg or 300 mg) daily in addition to their regularly prescribed anti-Parkinson medication for six weeks -- but those who took the 300 mg dose had significant improvements in Parkinson's Disease Questionnaire-39 total scores, and measures of quality of life such as activities of daily living, "stigma" and emotional well-being. No adverse effects were associated with the use of the CBD oil (Chagas, J Psychopharmacol 2014).
A preliminary trial found modest, dose-related improvements in symptoms of dystonia (involuntary muscle contractions) in five individuals taking between 100 mg and 500 mg per day of cannabidiol; however, at the highest dosages (300 mg to 500 mg) there was a worsening of tremor and the ability to initiate movement in two of the individuals who also had Parkinson's disease (Consroe, Int J Neurosci 1986).
Schizophrenia and psychosis Results in people with schizophrenia have been mixed. A study of high-dose CBD (500 mg taken morning and evening) among adults with schizophrenia found that adding CBD rather than placebo to existing treatments for six weeks reduced psychotic symptoms and caused a trend, although not statistically significant, toward improved performance on cognitive tasks. In this study, CBD was well tolerated with no increase in adverse effects (McGuire, Am J Psy 2017). Another 6-week study, however, found that 300 mg of CBD taken twice daily did not improve cognitive or psychotic symptoms in adults with schizophrenia on stable doses of medication; in fact, only those taking a placebo experienced a (modest) improvement in symptoms. Twenty percent of CBD-treated patients experienced sedation (mostly mild) compared to 5% of those on placebo (Boggs, Psychopharm 2018).
CBD seems to "partially normalize alterations" in areas of the brain that are implicated in psychosis (i.e., severely impaired thoughts and/or emotions). This was shown in a small, placebo-controlled study that measured activation of areas of the brain (based on blood flow measured with MRI imaging) during a verbal learning task. Brain activity in people at high risk of psychosis given a single dose of 600 mg of CBD more closely resembled that of people not at risk of psychosis than of people at risk of psychosis who were given a placebo. Interestingly, THC in marijuana can have the opposite effect and has been associated with the development and relapse of psychosis (Bhattacharyya, JAMA Psych 2018). A possible mechanism for an antipsychotic effect of CBD is that, at a dose of 600-800 mg per day, it seems to elevate natural levels of the endocannabinoid anandamide by moderately inhibiting its degradation (Rohleder, Front Pharmacol 2016).
Anxiety, PTSD, and sleep
CBD may reduce anxiety and symptoms of PTSD (post-traumatic stress syndrome). It may also improve sleep in people with such disorders and those with insomnia, but does not appear to be helpful as a sleep aid in healthy individuals.
Studies in animals as well as several small studies in people suggest CBD may help reduce anxiety. For example, a small placebo-controlled study in young healthy men found that a single 400 mg dose of CBD taken as a capsule reduced self-reported anxiety (but also increased feelings of mental sedation) one hour after ingestion (Crippa, Neuropsychopharmacology 2004). Studies have also found CBD to reduce anxiety with social speaking when given 90 minutes before speaking at a dose of 300 mg, while a lower dose (150 mg) was not effective and there were mixed results with a higher dose (600 mg) ((Bergamaschi, Neuropsychopharm 2011), Zuardi, J Psychopharmacol 1993, Linares, Braz J Psychiatr 2018). A study among Japanese teenagers with social anxiety found that 300 mg of CBD (which contained no THC and was in a base of MCT oil) daily for four weeks led to a modest decrease in symptoms while there was no significant change in symptoms among those given placebo (olive oil) (Masataka, Front Psychol 2019).
Case reports from an outpatient mental health clinic in Colorado suggested that even lower doses of CBD might be helpful with anxiety and related sleep disorders. (Bear in mind that case reports are not controlled studies, so these benefits remain to be proven.) In a group of 72 men and women treated with CBD daily for two months, anxiety scores decreased within the first month in 79.2% of patients and remained decreased during the study duration. Sleep scores improved within the first month in 66.7% but fluctuated over time. It's important to note that 15.3% reported a worsening of anxiety and 25% reported a worsening of sleep, and similar percentages were reported in the second month of supplementation. Most of the participants took one capsule daily containing 25 mg of CBD oil (provided by CV Sciences Inc., makers of PlusCBD Oil, although it was not a sponsor of the study), and continued taking their regularly prescribed medications. For anxiety, CBD was taken after breakfast, while, for sleep, it was taken after dinner. CBD was generally well-tolerated, although two patients discontinued treatment within the first week because of fatigue and three noted mild sedation that appeared to abate after a few weeks of treatment. CBD was discontinued for one patient with a developmental disorder in whom treatment appeared to cause disinhibition in the form of inappropriate sexual behavior (Shannon, Perm J 2019).
Another series of case reports from the clinic in Colorado suggested that CBD may help relieve symptoms of post-traumatic stress disorder (PTSD). In a group of 11 adults with diagnosed PTSD, overall symptoms decreased by an average of 28% over a 2-month period of CBD supplementation. The average daily CBD dose was 33.4 mg at the start, increasing to 44.6 mg by the end of the study. The participants took CBD as 25 mg capsules and/or an oral spray (1.5 mg of CBD per spray) (Elms, J Altern Complement Med 2019). Separately, the same clinic reported that CBD appeared to be helpful to a 10-year old girl with anxiety and sleep disorder due to PTSD caused by sexual abuse. She took 25 mg of CBD at bedtime and 6 mg to 12 mg of CBD from a sublingual spray as needed throughout the day for 5 months. Her anxiety and sleep improved to the extent that they were no longer classified as disorders (Shannon, Perm J 2016). Although no side effects were observed, it is important to note that there is concern that cannabinoids may affect brain development in children (See Concerns and Cautions).
Preliminary research suggested that CBD may affect the sleep-wake cycle, although this may depend on the dose and the condition for which it is taken. Low-dose CBD (15 mg) may have a stimulating effect, while moderate and higher doses can be sedating, and may improve sleep in people with anxiety (as in the case report above) and in those with certain sleep disorders (Babson, Curr Psychiatry Rep 2017). For example, a small study among 15 men and women with a history of insomnia found that 160 mg of CBD taken as a capsule 30 minutes before bedtime for one week significantly increased self-reported duration of sleep compared to placebo. Ten participants reported sleeping more than 7 hours after taking this dose of CBD, but when the same participants took a placebo, only six reported getting more than 7 hours of sleep. However, there was no decrease in the amount of time it took to fall asleep. Lower doses of CBD (40 mg and 80 mg) did not increase sleep time or reduce the amount of time it took to fall asleep (Carlini, J Clin Pharmacol 1981). None of the participants reported increased difficulty in waking or feeling sleepy upon awakening, compared to placebo.
On the other hand, an even greater dose of CBD -- 300 mg taken 30 minutes before bedtime, had no effect on the time it took healthy men to fall asleep. It also had no effect on the amount of time spent in each stage of sleep (such as REM sleep) or the amount of time participants stayed asleep (as measured by polysomnography), and it did not affect self-reported sleep quality, compared to placebo. CBD was not found to impair cognitive function when evaluated the following morning (Linares, Front Pharmacol 2018).
A study among 65 healthy, overweight men and women in the U.S. found that 15 mg of CBD from 60 mg of hemp oil extract (PlusCBD Extra Strength Hemp Extract, CV Sciences) taken as a softgel once daily with breakfast for six weeks did not improve sleep quality, mood, or ability to cope with stress compared to placebo. CBD supplementation modestly increased blood levels of "good" HDL cholesterol, but there were no changes in total or LDL cholesterol, body weight, blood pressure, or bodyweight compared to placebo. No increases in liver enzymes or serious adverse events were reported (Lopez, J Diet Suppl 2020). The hemp extract used in the study closely resembles that in Plus CBD Oil Hemp Softgels (60 mg hemp oil) tested and approved in this review.
Substance use disorder
High-dose CBD (400 mg or 800 mg of the prescription CBD oral solution Epidiolex) was shown to reduce drug cravings in a placebo-controlled study among 42 men and women with heroin use disorder, most of whom had been abstinent from heroin for less than one month. CBD was taken once daily for three days. CBD reduced cue-induced drug craving and anxiety and also reduced physiological measures of cue-induced craving such as increased heart rate compared to placebo one to two hours after the first dose of CBD as well as on the seventh day. Both doses of CBD equally reduced craving. There were no significant effects on cognition and no serious adverse events; mild side effects such as diarrhea, headache and fatigue were reported in both those taking CBD and placebo (Hurd, Am J Psychiatry 2019).
CBD may have helped a 17-year old male in Vienna, Austria with multiple substance use disorder (cannabis, MDMA, cocaine, ecstasy), severe depression, social phobia and narcissistic personality disorder. After unsuccessful treatment with the antidepressant sertraline for 6 months, he was started on a dose of 100 mg CBD (50 mg in the morning and evening), which, after 3 weeks, was gradually increased to 600 mg (300 mg twice daily), for a total treatment period of 8 weeks during which he also received, in a day clinic setting, group and individual psychotherapy, social cognition training, occupational therapy and physiotherapy, and his parents had weekly meetings with the treating psychiatrist. He reported no side effects from the CBD. He improved regarding depressive as well as anxiety symptoms and quit abusing illegal drugs without showing withdrawal symptoms (Laczkovics, Neuropsychiatr 2020).
Although there is some preliminary evidence that THC and, possibly other cannabinoids could potentially help to reduce interocular (eye) pressure in people with glaucoma, one study found that, four hours after ingestion, a single, sublingual dose of CBD (which also contained about 1 mg of THC) had no effect on interocular pressure, while a 40 mg dose of CBD (containing about 2 mg of THC) temporarily increased interocular pressure (Tomida, J Glaucoma 2006; Health Canada 2013). There do not appear to be longer-term studies, or studies investigating the effects of cannabidiol alone for glaucoma.
Pain Preliminary evidence suggests a role for CBD in pain management, but this role not been scientifically established in well-controlled studies in people. In many cases, studies have used combinations of THC with CBD rather than CBD alone or with minimal THC.
A study that showed promise with primarily CBD focused on people (ages 39 - 70) with chronic pain who had been on opioids for at least one year, although the study lacked a placebo control, so it is not possible to know if the effects were due to CBD. Study participants were given softgels of hemp extract (15.7 mg CBD and 0.5 mg THC per softgel, from Ananda Professional, which funded the study. [Note: In this Review, CL tested a different Ananda product that is "Zero THC"]. For eight weeks, most participants added two of the CBD softgels (a total of 31.4 mg of CBD) to their daily medication regimens. Among 94 patients who completed the study, 94% reported quality of life improvements and 53% reduced their use of opioids (three of whom completely eliminated opioids). CBD appeared to modestly reduce pain intensity and improve sleep quality. Although there were trends toward improvements in pain-related disability and overall health, these were not statistically significant. No significant adverse events were reported, but a small number of participants experienced nausea, heart burn, dry mouth, and/or nighttime anxiety, and two people did not complete the study due to drowsiness (Capano, Postgrad Med 2019).
One study found that an oral spray containing THC and CBD reduced pain in people with rheumatoid arthritis (Blake, Rheumatology (Oxford) 2006); however, a review of four short term clinical studies (including this one) investigating the effects of cannabinoids for the treatment of rheumatic diseases, including fibromyalgia syndrome, back pain, osteoarthritis and rheumatoid arthritis, concluded that there is "currently insufficient evidence to recommend cannabinoid treatments for management of rheumatic diseases pending further study." (Fitzcharles, Schmerz 2016). There do not appear to be any studies on the use of CBD alone for reducing pain in these conditions in people (although there are clinical trials suggesting a reduction in pain for dogs with osteoarthritis -- see CBD for Pets below).
A review of several experimental pain studies (using heat or pressure) on healthy people found that cannabis (marijuana) and cannabinoids may not reduce the intensity of pain, but may make pain feel less unpleasant and more tolerable. Although none of the studies tested CBD exclusively, the products containing CBD (in addition to THC), such as cannabis extracts, were shown to be more effective than those containing exclusively THC or THC analogues. The researchers suggested that CBD be investigated in future pain studies (De Vita, JAMA Psych 2018).
A few studies suggest that a combination of THC and CBD may be helpful for cancer-related pain; however, there do not appear to be studies on the effects of CBD alone for cancer-related pain (Blake, Ann Palliat Med 2017).
Preliminary evidence suggests that CBD may have anti-cancer properties and enhance the immune response to cancer. Although clinical studies have not been conducted, a case was reported in the UK of a man in his early 80s with lung cancer (biopsied as adenocarcinoma) who, after declining traditional therapies, had a dramatic reduction in tumor size after self-administering low-dose CBD twice daily (starting at just 1.32 mg of CBD twice daily for one week, and then 6 mg of CBD twice daily for another three weeks — each dose consisted of 9 drops (0.3 mL) of "MyCBD" oil labeled as 2% CBD. He took this daily dose again for a week after learning of the tumor reduction but stopped as he did not like the taste and it caused him slight nausea. A scan two months later showed the tumor remained stable in size. Further research is needed on CBD's effect on cancers (Sule-Suso, Sage Open Medical Case Reports, 2019). (For more information about cannabinoids and cancer treatment, see the National Cancer Institute's webpage about this topic.)
Colds, flu, viral infections
CBD has been promoted to fight colds, the flu, and even viral infection with Sars-CoV-2 (which causes COVID-19), but there is currently no clinical evidence to support these uses. In fact, when high doses of CBD (hundreds of milligrams per day) were given to children and young adults to determine CBD's anti-seizure effects (see Devinsky study, above), the number of upper respiratory infections reported was slightly higher among those who took CBD compared to placebo (11% vs. 8%, respectively).
Laboratories studies have shown that CBD can inhibit certain viruses, such as hepatitis C virus and Kaposi's sarcoma-associated herpesvirus (KSHV), but there is a lack of clinical research on CBD's effects on viral infections in people (Tagne, Cannabis Cannabinoid Res 2020). Generally, CBD seems to dampen immune system response to infection, decreasing inflammatory cytokines and the production of immune system cells in animal experiments (Nichols, Cannabis Cannabinoid Res 2020). For example, CBD has been shown to decrease the inflammatory response to infections such as pneumococcal meningitis (Barichello, Eur J Pharmacol 2012).
This dampening of the immune response could potentially have benefit in treating autoimmune diseases, as demonstrated in an experimental model of multiple sclerosis in mice (Kozela, Br J Pharmacol 2011). It could be hypothesized that this could also dampen the devastating "cytokine storm" that occurs in severe cases of COVID-19, but it far too early to know if this would be the case or whether it might make the infection worse.
Topical CBD Creams, gels and lotions containing CBD are often promoted to treat pain, such as muscle or joint pain. CBD appears to be better absorbed through the skin than THC (Huestis, Chem Biodivers 2007) and there is some evidence that in animals, creams and gels containing CBD may help reduce inflammation in conditions such as arthritis and multiple sclerosis (Hammell, Eur J Pain 2016; Giacoppo, Daru 2015). However, to date, clinical studies have not provided convincing evidence of a benefit with topical CBD. At best, topical CBD may provide a modest benefit to people suffering from intense forms of pain, with little demonstrated benefit in cases of less intense pain.
In a study of 13 young adults, CBD cream applied to the front thigh area after leg exercises (a series of squats) did not decrease delayed onset muscle soreness (DOMS) in the 48 hours following exercise compared to placebo (petroleum jelly). The cream contained 200 mg of CBD in each 1-oz. container (6.7 mg CBD/mL), which was shared among all of the participants, although the specific amount of cream or CBD was not specified (Garcia, Int J Exc Sci 2019 - Abstract plus correspondence with ConsumerLab). In the other study, a gel containing 10.5 mg or 21 mg of synthetic CBD was applied daily to the knees of people with knee osteoarthritis. Although both groups experienced reductions in "worst knee pain" scores, these reductions were not statistically significant compared to the reduction in pain scores for placebo group that used gel without CBD. Dryness at the site of application and headache were more frequent among those who used the CBD. The study was conducted by a company (Zynerba) seeking to develop the synthetic CBD (ZYN002) as a drug (Hunter, Osteoarthritis Cartilage 2018).
A preliminary study suggests that CBD cream may reduce certain symptoms of peripheral neuropathy, a condition characterized by nerve pain, burning, "pins and needles" sensations and weakness, typically in the hands and feet. In the study, 29 men and women (average age 68) with peripheral neuropathy of the lower extremities (feet and lower legs) due to type II diabetes, chemotherapy treatment, or other causes received one 3 fl. oz container of CBD cream blended with emu oil to enhance absorption (Theramu Relieve CBD compound cream -- 250 mg of CBD per container, 2.8 mg CBD/mL) or placebo cream (similar cream with emu oil but no CBD) and applied the cream to symptomatic areas up to four times daily for one month. Participants who used the CBD cream had modest, but statistically significant reductions in self-reported intense pain, sharp pain, cold and itchy sensations, but no reduction in hot, dull, sensitive, unpleasant, deep and surface pain, compared to placebo. No adverse events were reported. Theramu supplied the cream but did not fund the study (Xu, Curr Pharm Biotechnol 2019).
A clinical trial that suggested some benefit with topical CBD studied 60 young adults with temporomandibular disorder (jaw muscle pain from teeth grinding) in Poland. Participants rubbed a "pea-size" amount of ointment over their jaw muscles twice a day. For half the group, CBD Oil (Charlotte's Web Hemp Extract Oil in Olive Oil -- 67 mg CBD/mL) was added to the ointment (comprising 20% of the total ointment, making it 1.46% CBD, or about 7 mg of CBD per 0.5 gram application). After 14 days, jaw muscle activity at rest had decreased by about 12% in the CBD group versus only about 2% in control group, although this was not a statistically significant difference. Perhaps more importantly, the CBD group reported a 70% reduction in pain intensity versus only a 10% reduction for the control group, although the statistical significance of this difference was not determined (Nitecka-Buchta, J Clin Med 2019).
CBD for Pets:
Preliminary evidence suggests that short-term CBD supplementation may be of modest benefit to dogs with osteoarthritis. There is some concern, however, with the effects of CBD on liver enzymes in dogs and cats, as discussed below.
A study at Cornell University found that giving older dogs with osteoarthritis CBD, compared to placebo, for one month modestly reduced pain and increased activity levels (rising to standing, walking, running, and climbing) as reported by the dogs' owners, and reduced joint pain upon touch when examined by a veterinarian. However, there were no improvements in lameness or weight-bearing (i.e. reluctance to rise, favoring the affected leg when walking, or limping) as assessed by a veterinarian. The dose was 2 mg of an equal mix of CBD and CBDa per kg of bodyweight given twice daily (e.g., for a 20 lb dog: 18 mg of CBD/CBDa in the morning and again at night), and use of other regular supplements (e.g., glucosamine, fish oil, etc.) and NSAIDS was allowed. No side effects were reported with CBD but there was an increase in levels of the liver enzyme alkaline phosphatase, and the researchers recommended monitoring liver enzymes in dogs receiving CBD until long-term safety studies are conducted. The CBD (a hemp extract in olive oil) was provided by ElleVet Sciences, which funded the study (Gamble, Front Vet Sci 2018).
The same ingredient used in the above study was the subject of preliminary, 12-week, safety studies in young, healthy dogs and cats sponsored by the manufacturer. The dogs were given CBD as a softchew (ElleVet Mobility Chews by ElleVet Sciences) at a dose of 2 mg of CBD/CBDa per kg of bodyweight twice daily (e.g., 18 mg of CBD/CBDa in the morning and again at night for a 9 kg, or 20 lb, dog) and this did not significantly increase liver enzymes or cause adverse effects other than a low incidence of loose stool (3.3% of the time) and vomiting (<1% of the time). Food consumption and bodyweight remained consistent, and there were no abnormalities or changes in behavior noted. The cats were given the same ingredient as CBD-infused fish oil in capsules also at 2 mg CBD/CBDa per kg of bodyweight (e.g., for a 4 kg (9 lb) cat, 8 mg CBD/CBDa in the morning and again at night). One of the eight cats studied had a significant increase in a liver enzyme (alanine amino transferase, or ALT). The most common adverse effects were likely due to the capsules (some of which broke when being given to the cats) and included heavy salvation/drooling, excessive licking, gagging, and head shaking. There were no changes in food consumption, bodyweight or behavior. Interestingly, in cats, the bioavailability of CBD/CBDa was only about one-fifth of that in dogs, which would suggest either much lower absorption or faster elimination. The researchers concluded that "...CBD-rich hemp nutraceuticals appear to be safe in healthy adult dogs, while more work in cats is needed to fully understand utility and absorption." (Deabold, Animals (Basel) 2019).
A placebo-controlled study in large dogs with osteoarthritis found that 20 mg of CBD in a liposomal formulation or 50 mg of CBD alone taken daily for 4 weeks significantly decreased pain and increased mobility with no adverse effects on metabolism, hematocrit or other blood chemistry. The beneficial effect remained for at least 15 days after cessation of therapy. A 20-mg dose of CBD not in liposomal form was not effective. Additional laboratory research by the investigators indicated that CBD exhibited anti-inflammatory effects, reducing the production of tumor necrosis factor-alpha (TNF-a) and increasing the production of anti-inflammatory interleukin-10 (IL-10) (Verrico, Pain 2020).