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Cannabidiol (CBD) has been recently covered in the media, and you may have even seen it as an add-in booster to your post-workout smoothie or morning coffee. What exactly is CBD? Why is it suddenly so popular?

CBD stands for cannabidiol. It is the second most prevalent of the active ingredients of cannabis (marijuana). While CBD is an essential component of medical marijuana, it is derived directly from the hemp plant, which is a cousin of the marijuana plant. While CBD is a component of marijuana (one of hundreds), by itself it does not cause a "high." According to a report from the World Health Organization, "In humans, CBD exhibits no effects indicative of any abuse or dependence potential…. To date, there is no evidence of public health related problems associated with the use of pure CBD."

How is cannabidiol different from marijuana?

CBD may offer an option for treating different types of chronic pain. A study from the European Journal of Pain showed, using an animal model, CBD applied on the skin could help lower pain and inflammation due to arthritis. Another study demonstrated the mechanism by which CBD inhibits inflammatory and neuropathic pain, two of the most difficult types of chronic pain to treat. More study in humans is needed in this area to substantiate the claims of CBD proponents about pain control.

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Side effects of CBD include nausea, fatigue and irritability. CBD can increase the level in your blood of the blood thinner coumadin, and it can raise levels of certain other medications in your blood by the exact same mechanism that grapefruit juice does. A significant safety concern with CBD is that it is primarily marketed and sold as a supplement, not a medication. Currently, the FDA does not regulate the safety and purity of dietary supplements. So, you cannot know for sure that the product you buy has active ingredients at the dose listed on the label. In addition, the product may contain other (unknown) elements. We also don’t know the most effective therapeutic dose of CBD for any particular medical condition.

CBD has also been proposed to have antipsychotic effects and is considered a potential antipsychotic medicine, particularly due its relatively low side-effect profile [Zuardi et al. 1995]. Furthermore, it is also being developed as a possible ‘medicine’ for various other conditions, such as inflammation, diabetes, cancer and neurodegenerative diseases [Izzo et al. 2009].

Available evidence indicates that we do not yet have a complete understanding of the varied functions of the endocannabinoid system, which is widely distributed both in the brain and in the peripheral system and most glands and organs in the body. However, there has been a dramatic increase in research exploring this system during the last decade and it is considered to be one of the fastest growing fields in psychopharmacology, whilst the number of ‘classic’ neurotransmitter’ studies have either declined or remained the same [Pamplona and Takahashi, 2012]. Even though our knowledge on the role of the endocannabinoid system is still evolving, the available evidence indicates that this system has multiple regulatory roles in neuronal, vascular, metabolic, immune and reproductory systems. As mentioned previously, the on-demand regulatory role on other neurotransmitter systems clearly affect functions such as cognition, memory, motor movements and pain perception [Howlett et al. 2002].

In more recent years, three other novel receptor candidates, GPR18, GPR19 and GPR55, have been discovered, as well as non-CB1Rs and non-CB2Rs, but knowledge on these systems is incomplete and the discussion on whether or not they meet the criteria to qualify as receptors or channels is ongoing [Mackie and Stella, 2006; Pertwee et al. 2010; Pamplona and Takahashi, 2012]. It is generally established that some endocannabinoids, d-9-THC and several synthetic CB1R/CB2R agonists and antagonists can also interact with a number of non-CB1, non-CB2 GPCRs, ligand-gated ion channels and nuclear receptors (see the recent review by Pertwee and colleagues [Pertwee et al. 2010]). In conclusion, the biochemical mechanisms of this system are far more complex and the discussion on whether any known mammalian channel or non-CB1R/CB2R should be classified as a novel cannabinoid ‘CB3’ receptor or channel is ongoing.

Table 1.

The available research indicates that the main two compounds, d-9-THC and CBD, whilst having similar effects in certain domains, also have almost opposite effects to one another in other aspects [Carlini et al. 1974; Borgwardt et al. 2008; Fusar-Poli et al. 2009; Morrison et al. 2009; Bhattacharyya et al. 2009b; Winton-Brown et al. 2011]. Table 1 summarizes the varying effects of these two compounds.

In fact the different and opposing effects of the main two compounds of the plant were noticed in some early studies. In a double-blind study with 40 healthy volunteers, Karniol and colleagues orally administered d-9-THC and CBD and the mixtures of the two together, whilst pulse rate, time production tasks and psychological reactions were measured [Karniol et al. 1974]. Whilst d-9-THC alone increased pulse rate, disturbed time tasks and induced strong psychological reactions in the subjects, CBD alone provoked no such effects. However, CBD was efficient in blocking most of the effects of d-9-THC when both drugs were given together. CBD also decreased the anxiety component of d-9-THC effects in such a way that the subjects reported more pleasurable effects.

In relation to the imaging data, during the response inhibition task, relative to placebo, d-9-THC attenuated the engagement of brain regions that normally mediate response inhibition, whilst CBD modulated activity in regions not implicated with this task [Borgwardt et al. 2008]. During the verbal learning and retrieval of word pair tasks, d-9-THC modulated activity in mediotemporal and ventrostriatal regions, whilst CBD had no such effect [Bhattacharyya et al. 2009b]. During an emotional processing task d-9-THC and CBD had clearly distinct effects on the neural, electrodermal and symptomatic response to fearful faces [Fusar-Poli et al. 2009]. Our results suggest that the effects of CBD on activation in limbic and paralimbic regions may contribute to its ability to reduce autonomic arousal and subjective anxiety, whereas the anxiogenic effects of d-9-THC may be related to effects in other brain regions. During the auditory task, again these two compounds had opposite effects in the superior temporal cortex when subjects listened to speech and in the occipital cortex during visual processing [Winton-Brown et al. 2011].

When cannabis is used, d-9-THC as a partial agonist binds to CB1R and acts in a less selective manner in inhibiting the release of neurotransmitters normally modulated by endocannabinoids such as AEA and 2-AG. It has been putatively suggested that it may also increase the release of dopamine, glutamate and acetylcholine in certain brain regions, possibly by inhibiting the release of an inhibitory neurotransmitter like GABA onto dopamine, glutamate or acetylcholine-releasing neurons [Bhattacharyya et al. 2009a] ( Figure 2 ).