Systematic review maps CBD doses across 13 medical conditions, finding effective range from 1 to 50 mg/kg/day
Across 35 clinical studies in 13 conditions, effective CBD doses ranged from less than 1 to 50 mg/kg/day, with epilepsy showing the strongest evidence at around 15 mg/kg/day in RCTs.
Quick Facts
What This Study Found
23 of 35 studies reported significant improvement in primary outcomes. Epilepsy was the most studied condition (11 studies, all positive) with average RCT dose of 15 mg/kg/day. Studies of diabetes, Crohn's, ocular hypertension, fatty liver, and chronic pain found no positive effects, but used lower doses (average 2.4 mg/kg/day). No study reported plasma CBD concentrations.
Key Numbers
1,038 articles retrieved, 35 met inclusion criteria; 23 showed significant improvement; effective range <1 to 50 mg/kg/day; epilepsy average RCT dose ~15 mg/kg/day; conditions with negative results averaged 2.4 mg/kg/day; 0 studies reported plasma concentrations.
How They Did This
Systematic review searching PubMed, EMBASE, and ClinicalTrials.gov, identifying 35 studies across 13 medical contexts involving CBD-only administration.
Why This Research Matters
The absence of standardized CBD dosing guidance leaves patients and clinicians guessing. This review reveals that negative results may reflect underdosing rather than true inefficacy, especially for non-epilepsy conditions.
The Bigger Picture
The complete absence of pharmacokinetic data (no plasma concentration reporting) across 35 clinical studies is a striking gap. Without knowing how much CBD actually reaches the bloodstream, dose-response relationships remain guesswork.
What This Study Doesn't Tell Us
Could not conduct meta-analysis due to heterogeneity. Small sample sizes in many included studies (range n=6-62 for negative RCTs). No plasma concentration data available in any study. Publication bias possible.
Questions This Raises
- ?Would higher doses produce positive results in conditions where low doses failed?
- ?What plasma CBD concentrations are needed for therapeutic effects in different conditions?
Trust & Context
- Key Stat:
- No studies reported plasma levels
- Evidence Grade:
- Strong: comprehensive systematic review covering 35 studies across 13 medical conditions.
- Study Age:
- Published in 2019.
- Original Title:
- A systematic review of cannabidiol dosing in clinical populations.
- Published In:
- British journal of clinical pharmacology, 85(9), 1888-1900 (2019)
- Authors:
- Millar, S A, Stone, N L, Bellman, Z D, Yates, A S, England, T J, O'Sullivan, S E
- Database ID:
- RTHC-02181
Evidence Hierarchy
Analyzes all available research on a topic using a structured method.
What do these levels mean? →Frequently Asked Questions
What is the right dose of CBD?
It varies by condition. Epilepsy studies used around 15 mg/kg/day in RCTs. Conditions that failed to show benefit used much lower doses (average 2.4 mg/kg/day), suggesting they may have been underdosed.
Why is CBD dosing so confusing?
No clinical study has reported plasma CBD concentrations, and effective doses ranged from less than 1 to 50 mg/kg/day depending on the condition. This wide range, combined with CBD's variable absorption, makes dosing a major challenge.
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Cite This Study
https://rethinkthc.com/research/RTHC-02181APA
Millar, S A; Stone, N L; Bellman, Z D; Yates, A S; England, T J; O'Sullivan, S E. (2019). A systematic review of cannabidiol dosing in clinical populations.. British journal of clinical pharmacology, 85(9), 1888-1900. https://doi.org/10.1111/bcp.14038
MLA
Millar, S A, et al. "A systematic review of cannabidiol dosing in clinical populations.." British journal of clinical pharmacology, 2019. https://doi.org/10.1111/bcp.14038
RethinkTHC
RethinkTHC Research Database. "A systematic review of cannabidiol dosing in clinical popula..." RTHC-02181. Retrieved from https://rethinkthc.com/research/millar-2019-a-systematic-review-of
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.