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What are the side effects of CBD?

What are the side effects of CBD?

Explaining what CBD is and why it is a safe substance

CBD is a natural compound which comes from the Cannabis Sativa L plant. It offers various therapeutic properties which are endorsed by the World Health Organization (WHO)(1). Thanks to the anti-inflammatory, analgesic (pain relief), relaxing, anxiolytic (anxiety-reducing) and neuroprotective properties, among others, CBD and other cannabinoids are playing a key role in the development of new therapeutic and medicinal alternatives. Additionally, these cannabinoids also have low levels of toxicity in comparison with other drugs and they do not cause physical or psychological dependence. No-one has ever died as a direct result of a cannabis overdose, a fact that demonstrates the low toxicity of cannabinoids in general." Mariano Garcia de Palau, cannabis expert and vocal speaker at the Spanish Observatory of Medicinal Cannabis(2). In recent years, as people have become more open to the study and use of Cannabidiol, we have been able to treat many diseases, from insomnia, migraines, anxiety and depression to epilepsy and cancer. It has also proven to be an alternative medicine for inflammatory diseases, which are normally difficult to treat, such as arthritis, fibromyalgia, irritable bowel syndrome and more chronic illnesses characterised by inflammation, pain and/or restricted movement such as trauma and neurodegenerative diseases.

Side effects of CBD


  • Studies on Cannabidiol are relatively recent. Therefore, there are not many studies which look at the effects of its long-term use.
  • Many of the studies on the toxicity of CBD are carried out in-vitro or in vivo, i.e in laboratories and on animals. Therefore, studies on humans are limited.
  • Almost all studies use CBD isolated in crystals of 99% purity, which is considered to be a very safe substance according to WHO(1). However, there are many CBD oils with a “full spectrum” formula, which means that the extraction retains other components of hemp in small quantities and although the concentration is very low, these components could have other adverse effects.

¿Nevertheless, almost all CBD studies, as well as human clinical evidence, show that CBD is a very safe substance provided that it is used in the right way. CBD has very low toxicity and very few side effects, even when using relatively big amounts (up to 1500 mg per day)(3)(4). It’s also worth noting that some effects of CBD may be considered adverse or beneficial depending on the particular context and situation of each person, as well as the time of day. For example, CBD’s relaxing effect can be beneficial for a hyperactive person or someone who suffers from muscle spasms or insomnia, while this might be considered unfavourable for people with high blood pressure or depression, or anyone who needs to stay attentive and alert, like someone who works with dangerous equipment.

  • Dry mouth
  • Constipation
  • Changes in appetite
  • Nausea and/or diarrhea
  • Exhaustion
  • Dizziness
  • Drop in blood pressure

In a survey carried out by Project CBD (Cultivating Wellness), 40% of participants noticed one or more adverse effects. The findings of the survey revealed that these adverse effects were moderate with the most typical being dry mouth (18% of participants), then drowsiness (12%), dry and/or red eyes (5%) and increase in appetite (5%). Hay que destacar que prácticamente todos los efectos secundarios son temporales y limitados a las tomas de CBD por lo tanto su duración, aunque dependa de la vía de administración utilizada, va desde 10 minutos hasta unas horas.

Para saber más sobre los diferentes formatos y su respectiva duración, echa un vistazo a nuestro artículo; "¿Cuál es la mejor forma de usar CBD para ti?"

Effects on the digestive system

CBD interacts with the cannabinoid receptors in the mouth, which temporarily reduces the production of saliva, especially if the CBD is inhaled. The resulting dry mouth is only temporary and can be alleviated by drinking or sucking on a sweet. (2) In the majority of studies carried out on humans, CBD has been ingested. These studies have shown that ingesting CBD can affect the secretion of gastric juices and cause the bowels to empty more slowly, which means that some people who ingest CBD frequently have a tendency to experience constipation (2) or a decreased appetite(5)(6). When CBD is ingested, some people may suffer from nausea and/or diarrhea(6). However, in most cases this is due to an intolerance to the carrier oil (hemp oil, coconut oil, etc.) or because of the impurity of the extract used (which may contain chemical residues), in addition to a possible reaction to other medication(7). Summary: Any unwanted side effects on the digestive system are very infrequent and are almost exclusively associated with the oral ingestion of CBD.
People who do experience any of these side effects could opt for the inhalation of CBD (the only side effect of which can be resolved easily) or better yet the sublingual route, carried out in the correct way (under the tongue for 60-90 seconds), before then trying to spit out what is left of the CBD rather than ingesting it.

Effects on the liver - Interaction with other medication

In sole regard to the oral ingestion of CBD, the effects on the liver have arguably been studied the most because of their importance in the medical field. Due to its absorption in the liver, CBD interacts with metabolising enzymes in the Cytochrome P450 group(3)(4)(5), which are responsible for the absorption of most medications. This interaction causes a change in the metabolism of some drugs and an increase in their level in the blood(2), with a possible increase in their effects(6). When CBD is ingested, some people may suffer from nausea and/or diarrhea(6). However, in most cases this is due to an intolerance to the carrier oil (hemp oil, coconut oil, etc.) or because of the impurity of the extract used (which may contain chemical residues), in addition to a possible reaction to other medication(7). Summary: The oral ingestion (not sublingual) of CBD is the only way in which people may experience side effects in the liver and although they aren’t necessarily an issue for most people, they can be problematic for anyone who takes other medication that CBD could interact with. Therefore, if someone is taking other medication, it is advised that they consult a specialist who can monitor the existence of any drug interaction and act accordingly, given that there are some medicines that cannot be used alongside CBD.
Hematological and physiological changes
Hematological, biochemical and physiological changes, which can affect the entire body, have been observed in some studies on CBD. One should note that these changes may become more serious particularly when using very high doses and ingesting through the mouth(3)(4)(5)(6). Summary: Hematological and physiological changes are the only side effects that appear over time, after having ingested CBD on several occasions. In general, these side effects are positive. The unwanted side effects observed in these investigations, in addition to being highly improbable, occur in animals when the CBD dosage is very high and ingested orally. The relaxing and anxiolytic (anxiety-reducing) properties of CBD are, above all, due to the fact that it can cause hypotension (lowering of the blood pressure). Although this side effect can be considered beneficial and therapeutic in regard to anxiety, insomnia or muscle cramps, in some cases it could be considered a negative side effect due to feelings of tiredness or drowsiness(5)(6). It could also potentially cause dizziness because of drops in blood pressure(2). Therefore, people with very low blood pressure or those who take medication to moderate their blood pressure should take particular care, as well as anyone who needs to remain constantly alert, for example, when operating dangerous machinery. One should also consider those feelings of drowsiness and sedation(5) are brought on most strongly by drug interaction, especially with Central Nervous System depressants, including alcohol(6). Summary: The relaxing side effect of CBD, as well as the effect which lowers blood pressure, are in fact the most important therapeutic properties of CBD. However, these effects can be undesirable for people who suffer from hypotension or anyone who needs to pay particular attention during a specific activity or job.
Therefore, people who want to reduce this side effect should use a lower dose of CBD, although this will also lessen its therapeutic effect. With this in mind, it’s important that each individual weighs up all the benefits and risks and chooses the correct dosage for them.

The side effects associated with each route of CBD administration

Sublingual use (“Under the tongue”)

Administering CBD sublingually means you can avoid most of the side effects previously mentioned. Although it may cause temporary dry mouth, it is the most recommended way to take CBD to enjoy a stable and continuous effect. However, the relative difficulty of fully absorbing all of the oil droplets means that one should also check for possible side effects related to the ingestion of CBD. Additionally, sublingual administration can also lead to a lowering of blood pressure and possible tiredness and drowsiness.


Inhaling CBD also helps avoid the majority of adverse effects related to ingestion, although it may cause temporary dry mouth.
In any case, as inhaling CBD is fast-acting— it produces near-immediate effects because it passes quickly from the lungs into the blood—one should be careful of possible drops in blood pressure or slight dizziness that can occur, especially if a high concentration is used.
Moreover, the feeling of tiredness and drowsiness can be accentuated when inhaling CBD, particularly in the first 15-30 minutes.

Oral Ingestion

The vast majority of studies have looked into the oral ingestion of CBD, demonstrating that this route of administration has the highest risk of adverse effects, including all of the side effects aforementioned. In addition to being the only form of administration that could interact with other medication, ingesting CBD also involves an erratic absorption of CBD itself, which makes it difficult for the user to enjoy a stable effect.


CBD topicals do not cause any side effects (beyond possible allergic reactions), as its effect is limited to the area of application. Unlike topical products (such as creams, lotions and balms), transdermal patches do affect your system as they deliver CBD directly into the bloodstream. Therefore, they may cause possible adverse effects related to drops in blood pressure and the feeling of tiredness or drowsiness. One should be aware, therefore, that using a transdermal patch is not the same as using a topical product.
To find out more about the different routes of CBD administration, take a look at our article: What’s the best way to take your CBD?


  1. CANNABIDIOL (CBD) Pre-Review Report. Expert Committee on Drug Dependence. Thirty-ninth Meeting. Geneva, 6-10 November. 2017
  2. Principales efectos secundarios del CBD. Mariano de García Palau. Fundación Canna
  3. Bergamaschi MM, Queiroz RH, Zuardi AW, Crippa JA. Safety and side effects of cannabidiol, a Cannabis sativa constituent. Curr Drug Saf. 2011 Sep 1;6(4):237-49. doi: 10.2174/157488611798280924. PMID: 22129319.
  4. Iffland K, Grotenhermen F. An Update on Safety and Side Effects of Cannabidiol: A Review of Clinical Data and Relevant Animal Studies. Cannabis Cannabinoid Res. 2017 Jun 1;2(1):139-154. doi: 10.1089/can.2016.0034. PMID: 28861514; PMCID: PMC5569602.
  5. Brown JD, Winterstein AG. Potential Adverse Drug Events and Drug-Drug Interactions with Medical and Consumer Cannabidiol (CBD) Use. J Clin Med. 2019;8(7):989. Published 2019 Jul 8. doi:10.3390/jcm8070989
  6. Huestis MA, Solimini R, Pichini S, Pacifici R, Carlier J, Busardò FP. Cannabidiol Adverse Effects and Toxicity. Curr Neuropharmacol. 2019;17(10):974-989. doi: 10.2174/1570159X17666190603171901.
  7. https://www.sps.nhs.uk/articles/cannabidiol-oil-potential-adverse-effects-and-drug-interactions/
  8. Urits I, Borchart M, Hasegawa M, Kochanski J, Orhurhu V, Viswanath O. An Update of Current Cannabis-Based Pharmaceuticals in Pain Medicine. Pain Ther. 2019 Jun;8(1):41-51. doi: 10.1007/s40122-019-0114-4

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Author information

Neuropsychologist | Specialised in treatments with Medical Cannabis

Tommaso Bruscolini

Tommaso Bruscolini (Rimini, Italy) is a neuropsychologist and phytotherapist based in Barcelona, where he has been running his private practice since 2014, both in person and online, where he formulates and produces different preparations with all kinds of medicinal plants, as well as making personalised recommendations.

A member of the Official College of Psychologists of Catalonia and qualified as a Health Psychologist, he is a specialist in Neuropsychology, the branch that studies the brain and its neurological function. Tommaso complements his training with studies in Phytotherapy and Herbalism at the Guild of Herbalists of Catalonia and two Masters, one in Nutrition and Herbal Dietetics and the other in Mindfulness.

In recent years she has specialised in Medical Cannabis, through private training and collaborations with different entities in the world of Medical Cannabis, coordinating for a year a clinic specialising in cannabinoid medicine, carrying out consultations, writing articles, talks, training courses as well as carrying out consultations and patient follow-up.

He currently collaborates with several entities of the cannabis sector in Spain, among other things he is the coordinator of the therapeutic area of the magazine DolceVita España, consultant in the SmokingMap portal, collaborator of the Unión de Pacientes por la Regulación del Cannabis (UPRC) and Alpha-Cat certified technician to perform cannabinoid analysis.

What fascinates him most about the Cannabis plant is the possibility it has to change the current medicinal and therapeutic paradigm towards a more holistic vision as it acts on our body, mind and mood, in a synergic way.

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