Product Reviews
CBD & Hemp Extract Supplements Review

Initial Posting: 2/8/18  Last Update: 1/15/19
CBD and Hemp Oils Reviewed by

Sections: Jump to a section by clicking on its name.
  • 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 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, all 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 (See What It Is and What It Does).
  • What did CL find? ConsumerLab found the dose of CBD per suggested serving ranged 10-fold from 2.2 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. (See What CL Found and use the Results table to compare the amounts of CBD and other cannabinoids in products).
  • Top Picks ConsumerLab selected a Top Pick for People and a Top Pick for Pets based on top quality and value.
  • What to look for? If you seek CBD, look for products that list the amount of CBD per serving. 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.

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). 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% occured 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).

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, 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).

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).

Studies in animals as well as several small studies in people suggest CBD may help reduce anxiety. For example, a small 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, compared to placebo (Crippa, Neuropsychopharmacology 2004). A study that found CBD reduced anxiety with social speaking utilized a single dose of 600 mg of CBD given 90 minutes before speaking (Bergamaschi, Neuropsychopharm 2011) and a similar study showed reduced anxiety using a dose of 300 mg (Zuardi, J Psychopharmacol 1993). A more recent study among 57 men in Brazil found that a dose of 300 mg of CBD taken approximately 90 minutes before public speaking significantly reduced self-reported anxiety during speaking compared to placebo, but a lower (150 mg) and higher (600 mg) dose did not reduce anxiety. None of the doses of CBD increased self-reported drowsiness or cognitive impairment (Linares, Braz J Psychiatr 2018). In a 10 year old girl with anxiety and sleep disorders due to post traumatic stress disorder (PTSD) caused by sexual abuse, 25 mg of CBD taken at bedtime, and 6 mg to 12 mg of CBD sublingual spray taken as needed throughout the day for 5 months improved her anxiety and sleep 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).

Lower-dose CBD supplementation was generally reported to improve symptoms of anxiety and mildly improve sleep in a group of 72 men and women who took CBD for one to two months as part of their treatment for anxiety and sleep disorders. This was not a controlled or blinded study, but findings from an outpatient mental health clinic in Colorado. 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. 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. During the first month of supplementation 15.3% reported a worsening of anxiety, and 25%, a worsening of sleep, and similar percentages were reported in the second month of supplementation. 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). As discussed below, evidence that CBD improves sleep is mixed, and studies showing a benefit have typically used a higher dose.

Preliminary research suggests 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. 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).

CBD did not seem to affect sleep in a study of 27 healthy men and women (average age 30) who did not have sleep or psychiatric disorders: A single 300 mg dose of CBD taken 30 minutes before bedtime had no effect on the time it took to fall asleep, 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).

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.

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.

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). (For more information about cannabinoids and cancer treatment, see the National Cancer Institute's webpage about this topic.)

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, there are no studies on the effects of topical CBD creams, gels or lotions in people.

CBD for Pets:
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 CBD per kg of bodyweight given twice daily (e.g., for a 20 lb dog: 18 mg of CBD in the morning and again at night), and other regular supplementation was allowed to continue (e.g., glucosamine, fish oil, etc.). 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).

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