Cannabidiol — The Sunlight Experiment

Pharmacology & Research

Cannabidiol is the non-intoxicating counterpart to THC and the dominant cannabinoid in most hemp. Its pharmacology is unusual: it barely touches the CB1 receptor that drives the cannabis “high,” and instead works through a scatter of other targets — serotonin 5-HT1A receptors, TRPV vanilloid channels, the enzyme FAAH (which raises the body’s own endocannabinoids), GPR55 and PPARγ. That broad, indirect profile is why CBD turns up in so many contexts, and why its evidence is strongest where it has been tested as a purified pharmaceutical rather than a wellness oil. One purified formulation (Epidiolex) is an approved anti-seizure medicine ^{1,2,3Reference 1Devinsky O et al. · 2017RCTTrial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trialView study →Reference 2Devinsky O et al. · 2018RCTEffect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trialView study →Reference 3Thiele EA et al. · 2018RCTCannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4) — randomised controlled trialView study →}.

What the evidence supports

Best-supported: purified CBD reduces seizures in Dravet and Lennox-Gastaut epilepsy syndromes — the basis of its FDA/EMA approval ^{1,2,3Reference 1Devinsky O et al. · 2017RCTTrial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trialView study →Reference 2Devinsky O et al. · 2018RCTEffect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trialView study →Reference 3Thiele EA et al. · 2018RCTCannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4) — randomised controlled trialView study →}.
Emerging, worth watching: single high doses ease acute anxiety ^{4Reference 4Bergamaschi MM et al. · 2011RCTCannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients — randomised controlled trialView study →}; 400–800 mg/day reduces use in cannabis use disorder ^{5Reference 5Freeman TP et al. · 2020RCTCannabidiol for the treatment of cannabis use disorder: a phase 2a, double-blind, placebo-controlled, randomised trialView study →}; symptom (not mucosal) improvement in Crohn’s disease ^{6Reference 6Naftali T et al. · 2021RCTOral CBD-rich Cannabis Induces Clinical but Not Endoscopic Response in Patients with Crohn’s Disease — randomised controlled trialView study →}.
The preparation gap: these results come from 300 mg–20 mg/kg purified CBD; typical 10–50 mg retail products sit far below the studied doses.
Bioavailability is the catch: oral CBD is poorly and erratically absorbed (~6%), and a fatty meal can multiply exposure several-fold ^{7Reference 7Millar SA et al. · 2018Systematic reviewA Systematic Review on the Pharmacokinetics of Cannabidiol in Humans — review of human PKView study →}.

0. Evidence by application

Support is an experimental score — a composite weighted by study type (human > animal > in vitro) and volume, tempered for isolate-vs-plant match and dose realism. A beta, not a validated metric. Each application links to its write-up.

Application	Support	Rests on
Drug-resistant epilepsy	█████████░ 88%	Pivotal placebo-controlled RCTs of purified CBD; FDA/EMA-approved (Epidiolex) ^{1,2,3Reference 1Devinsky O et al. · 2017RCTTrial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trialView study →Reference 2Devinsky O et al. · 2018RCTEffect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trialView study →Reference 3Thiele EA et al. · 2018RCTCannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4) — randomised controlled trialView study →}
Anxiety	█████░░░░░ 50%	Small RCTs at 300–600 mg in acute-stress/social-anxiety models ^{4Reference 4Bergamaschi MM et al. · 2011RCTCannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients — randomised controlled trialView study →}
Cannabis use disorder	█████░░░░░ 45%	One well-conducted phase 2a RCT, positive ^{5Reference 5Freeman TP et al. · 2020RCTCannabidiol for the treatment of cannabis use disorder: a phase 2a, double-blind, placebo-controlled, randomised trialView study →}
Inflammatory bowel disease	████░░░░░░ 44%	RCT: symptom & quality-of-life gains, no mucosal healing ^{6Reference 6Naftali T et al. · 2021RCTOral CBD-rich Cannabis Induces Clinical but Not Endoscopic Response in Patients with Crohn’s Disease — randomised controlled trialView study →}

1. Drug-resistant epilepsy

CBD’s strongest evidence by far. In placebo-controlled trials of purified CBD added to existing anti-seizure drugs, convulsive seizures in Dravet syndrome fell about 39% versus 13% on placebo ^{1Reference 1Devinsky O et al. · 2017RCTTrial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trialView study →}, and drop-seizures in Lennox-Gastaut syndrome fell roughly 42–44% versus ~17–22% at 10–20 mg/kg/day ^{2,3Reference 2Devinsky O et al. · 2018RCTEffect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trialView study →Reference 3Thiele EA et al. · 2018RCTCannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4) — randomised controlled trialView study →}. This is what led to Epidiolex’s approval for these rare syndromes (and tuberous sclerosis).

Gap: proven only for specific paediatric syndromes with prescription-grade CBD at high mg/kg doses — it doesn’t generalise to epilepsy broadly or to consumer CBD oils, and a clobazam interaction and liver-enzyme rises need monitoring (see Safety).

2. Anxiety

The calming reputation belongs to CBD specifically (high-THC cannabis can do the opposite). In a double-blind RCT, a single 600 mg oral dose reduced anxiety during a simulated public-speaking test in people with social anxiety disorder ^{4Reference 4Bergamaschi MM et al. · 2011RCTCannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients — randomised controlled trialView study →}, and several smaller acute-dosing studies point the same way.

Gap: the evidence is small, acute-challenge studies at 300–600 mg — far above retail doses — with no large trial of sustained dosing for a diagnosed anxiety disorder ^{4Reference 4Bergamaschi MM et al. · 2011RCTCannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients — randomised controlled trialView study →}.

3. Cannabis use disorder

Counterintuitively, CBD shows promise for helping people cut down on cannabis itself. In a phase 2a double-blind RCT, 400 mg and 800 mg daily beat placebo on measures of cannabis use in people with moderate-to-severe cannabis use disorder ^{5Reference 5Freeman TP et al. · 2020RCTCannabidiol for the treatment of cannabis use disorder: a phase 2a, double-blind, placebo-controlled, randomised trialView study →}.

Gap: a single well-designed trial — a credible signal awaiting replication at scale ^{5Reference 5Freeman TP et al. · 2020RCTCannabidiol for the treatment of cannabis use disorder: a phase 2a, double-blind, placebo-controlled, randomised trialView study →}.

4. Inflammatory bowel disease

An RCT of oral CBD-rich cannabis in Crohn’s disease produced clinical and quality-of-life improvement — but without endoscopic (mucosal) healing ^{6Reference 6Naftali T et al. · 2021RCTOral CBD-rich Cannabis Induces Clinical but Not Endoscopic Response in Patients with Crohn’s Disease — randomised controlled trialView study →}, the recurring pattern for cannabis in IBD: symptoms ease while the underlying inflammation is unchanged.

Gap: symptomatic and quality-of-life benefit only; no evidence it modifies the disease, so it doesn’t replace standard IBD therapy ^{6Reference 6Naftali T et al. · 2021RCTOral CBD-rich Cannabis Induces Clinical but Not Endoscopic Response in Patients with Crohn’s Disease — randomised controlled trialView study →}.

Mechanisms

Target / pathway	Effect	Relevant to
5-HT1A (serotonin) agonism	anxiolytic, anti-nausea	anxiety
TRPV1/TRPV2 vanilloid agonism	anti-inflammatory, analgesic	IBD, pain
FAAH inhibition → ↑ anandamide	indirect endocannabinoid tone	anxiety, broad
GPR55 antagonism; Ca²⁺-channel modulation	anticonvulsant	epilepsy
PPARγ activation	anti-inflammatory, neuroprotective	broad

Pharmacokinetics

CBD’s practical weak point is absorption. A systematic review of human CBD pharmacokinetics found oral bioavailability is low and highly variable — on the order of ~6% — because of poor water solubility and extensive first-pass metabolism, and a high-fat meal can raise exposure several-fold (the “food effect”) ^{7Reference 7Millar SA et al. · 2018Systematic reviewA Systematic Review on the Pharmacokinetics of Cannabidiol in Humans — review of human PKView study →}. Reported half-life varies widely with route and regimen. The upshot: dose alone is a poor guide to what reaches the blood, and formulation and whether it’s taken with food matter as much as milligrams ^{7Reference 7Millar SA et al. · 2018Systematic reviewA Systematic Review on the Pharmacokinetics of Cannabidiol in Humans — review of human PKView study →}.

Clinical trials

CBD has an unusually large trial footprint for a plant compound, concentrated in epilepsy (where a purified product is licensed) with a growing spread into anxiety, substance use, inflammation and pain.

Completed	Planned	Terminated	Preclinical
Many (epilepsy-led)	Several	—	Extensive

Last checked: July 2026.

Toxicity & Safety

CBD is well tolerated, with the commonest effects being drowsiness, diarrhoea and appetite change ^{1,2Reference 1Devinsky O et al. · 2017RCTTrial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trialView study →Reference 2Devinsky O et al. · 2018RCTEffect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trialView study →}. The interactions matter more than the side effects. CBD inhibits several cytochrome-P450 enzymes (CYP3A4, CYP2C9, CYP2C19, CYP2D6, CYP1A2), so it can raise blood levels of co-administered drugs — a controlled study showed CBD roughly tripled exposure to the active metabolite of the epilepsy drug clobazam via CYP2C19 inhibition ^{8Reference 8Morrison G et al. · 2019A Phase 1 Open-Label Trial of Drug-Drug Interactions Between Clobazam, Stiripentol or Valproate and Cannabidiol in Healthy Subjects — human pharmacokinetic studyView study →}. And high-dose CBD can raise liver enzymes: in healthy adults given 1,500 mg/day, ALT rose above normal in nearly half and met drug-induced-liver-injury thresholds in about a third, resolving on stopping ^{9Reference 9Watkins PB et al. · 2021Clinical trialCannabidiol and Abnormal Liver Chemistries in Healthy Adults: Results of a Phase I Clinical Trial — human trialView study →}. Anyone on regular medication should check for interactions before use, and the unregulated supplement market means product content varies.

Pregnancy & lactation

Avoid. CBD is a component of cannabis, which is not recommended in pregnancy or breastfeeding; cannabinoids cross the placenta and enter breast milk, and there are no controlled safety data for purified CBD in these groups. Prudent to avoid.

Dosage

Studied doses span a wide range depending on the goal — and they sit well above typical wellness products. These are doses studied in research, not a recommendation, and high-dose use is a medical decision given the interactions above.

Application	Form	Dose (studied)	Source
Drug-resistant epilepsy	Purified CBD oral solution	10–20 mg/kg/day	^{1,2,3Reference 1Devinsky O et al. · 2017RCTTrial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trialView study →Reference 2Devinsky O et al. · 2018RCTEffect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trialView study →Reference 3Thiele EA et al. · 2018RCTCannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4) — randomised controlled trialView study →}
Anxiety (acute)	Purified CBD, single oral dose	300–600 mg	^{4Reference 4Bergamaschi MM et al. · 2011RCTCannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients — randomised controlled trialView study →}
Cannabis use disorder	Purified CBD, daily	400–800 mg/day	^{5Reference 5Freeman TP et al. · 2020RCTCannabidiol for the treatment of cannabis use disorder: a phase 2a, double-blind, placebo-controlled, randomised trialView study →}

References

Devinsky O, Cross JH, Laux L, et al. (2017). Trial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome — randomised controlled trial. New England Journal of Medicine. https://pubmed.ncbi.nlm.nih.gov/28538134/
Devinsky O, Patel AD, Cross JH, et al. (2018). Effect of Cannabidiol on Drop Seizures in the Lennox-Gastaut Syndrome — randomised controlled trial. New England Journal of Medicine. https://pubmed.ncbi.nlm.nih.gov/29768152/
Thiele EA, Marsh ED, French JA, et al. (2018). Cannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4) — randomised controlled trial. The Lancet. https://pubmed.ncbi.nlm.nih.gov/29395273/
Bergamaschi MM, Queiroz RH, Chagas MH, et al. (2011). Cannabidiol reduces the anxiety induced by simulated public speaking in treatment-naive social phobia patients — randomised controlled trial. Neuropsychopharmacology. https://pubmed.ncbi.nlm.nih.gov/21307846/
Freeman TP, Hindocha C, Baio G, et al. (2020). Cannabidiol for the treatment of cannabis use disorder: a phase 2a, double-blind, placebo-controlled, randomised trial. The Lancet Psychiatry. https://pubmed.ncbi.nlm.nih.gov/32735782/
Naftali T, Bar-Lev Schleider L, Almog S, et al. (2021). Oral CBD-rich Cannabis Induces Clinical but Not Endoscopic Response in Patients with Crohn’s Disease — randomised controlled trial. Journal of Crohn’s & Colitis. https://pubmed.ncbi.nlm.nih.gov/33858011/
Millar SA, Stone NL, Yates AS, O’Sullivan SE (2018). A Systematic Review on the Pharmacokinetics of Cannabidiol in Humans — review of human PK. Frontiers in Pharmacology. https://pubmed.ncbi.nlm.nih.gov/30534073/
Morrison G, Crockett J, Blakey G, Sommerville K (2019). A Phase 1 Open-Label Trial of Drug-Drug Interactions Between Clobazam, Stiripentol or Valproate and Cannabidiol in Healthy Subjects — human pharmacokinetic study. Clinical Pharmacology in Drug Development. https://pubmed.ncbi.nlm.nih.gov/30791225/
Watkins PB, Church RJ, Li J, Knappertz V (2021). Cannabidiol and Abnormal Liver Chemistries in Healthy Adults: Results of a Phase I Clinical Trial — human trial. Clinical Pharmacology & Therapeutics. https://pubmed.ncbi.nlm.nih.gov/33022751/

Where Does It Come From? (1)