Table 2.

Adverse events and estimated event rates for medical cannabinoids, with GRADE of evidence rated high

TYPE OF ADVERSE EVENT	CANNABINOID EVENT RATE, %	PLACEBO EVENT RATE, %	NNH
Overall	81	62	6
Withdrawal due to adverse events	11	Approximately 3%	14
Serious adverse events	NS	NS	NS
Central nervous system effects	60	27	4
“Feeling high”	35	3	4
Sedation	50	30	5
Speech disorders	32	7	5
Dizziness	32	11	5
Ataxia or muscle twitching	30	11	6
Numbness	21	4	6
Disturbance in attention or disconnected thoughts	17	2	7
Hypotension	25	11	8
Dysphoria	13	0.3	8
Psychiatric	17	5	9
Euphoria	15	2	9
Impaired memory	11	2	12^*
Disorientation or confusion	9	2	15
Blurred vision or visual hallucination	6	0	17
Dissociation or acute psychosis	5	0	20

GRADE—Grading of Recommendations Assessment, Development and Evaluation, NNH—number needed to harm, NS—not statistically significant. Data from accompanying systematic review by Allan et al (page e78).¹² Examples of harms were selected from the largest statistically significant meta-analyses providing event rates. Grouping of adverse events follows the combinations used in the original research.¹²
↵* Confidence intervals suggest that harm is likely (risk ratio = 3.41, 95% CI 0.95–12.27), so estimated NNH provided.