Systematic review maps CBD doses across 13 medical conditions, finding effective range from 1 to 50 mg/kg/day | Research

The takeaway

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.

CBD users, prescribers, product formulators, and clinical trial designers.

No studies reported plasma levels

What the researchers 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.

Why it 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 numbers in context

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 the study worked

Systematic review searching PubMed, EMBASE, and ClinicalTrials.gov, identifying 35 studies across 13 medical contexts involving CBD-only administration.

What this study cannot 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.

How to read the evidence

Strong: comprehensive systematic review covering 35 studies across 13 medical conditions.

When this study was published

Published in 2019.

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.

Questions still open

Would higher doses produce positive results in conditions where low doses failed? What plasma CBD concentrations are needed for therapeutic effects in different conditions?

Common 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.

Read the original research

A systematic review of cannabidiol dosing in clinical populations.

British journal of clinical pharmacology, 85(9), 1888-1900

View on PubMed ↗Publisher’s paper ↗

Citation

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