How to give advice for lower-risk cannabis use


As a parent, sometimes I have given overly-cautious advice like: “The only way to guarantee not having a ‘drug problem’ is to not use drugs.” While the statement is true, it is totally useless advice for those who choose to experiment or consume a psychoactive drug with the potential for problem use.1 A better approach is to provide factual, evidence-based guidelines after the “overly-cautious advice.”

Fortunately, Fischer et al. provide just that: evidence-based guidelines for lower-risk consumption of cannabis.2 The selected studies were rated according to the following evidence grades (i.e., same criteria as used by the National Academies of Sciences, Engineering, and Medicine):3

Grading Criteria
1. Conclusive based on good-quality studies and no credible opposing findings;
2. Substantial based on several supportive findings from good-quality studies with few opposing studies;
3. Moderate based on several supportive findings from good- to fair-quality studies with few or no credible opposing findings; a general conclusion can be made, but limitations, including chance, bias, and confounding factors, cannot be ruled out;
4. Limited supportive findings from fair-quality studies or mixed findings with most favoring one conclusion, or no firm conclusions; and
5. None or Insufficient based on mixed findings, a single poor study, or the endpoint has not been studied, with substantial uncertainty attributable to chance, bias, and confounding factors.


Recommendation 1:

The most effective way to avoid any risks of cannabis use is to abstain from use. Those who decide to use need to recognize that they incur risks of a variety of—acute and long-term—adverse health and social outcomes. These risks will vary in their likelihood and severity with user characteristics, use patterns, and product qualities, and so may not be the same from user to user or use episode to another. [Evidence Grade: None required.]

Recommendation 2:

Early initiation of cannabis use (i.e., most clearly that which begins before age 16 years) is associated with multiple subsequent adverse health and social effects in young adult life. These effects are particularly pronounced in early-onset users who also engage in intensive and frequent use. This may be in part because frequent cannabis use affects the developing brain. Prevention messages should emphasize that, the later cannabis use is initiated, the lower the risks will be for adverse effects on the user’s general health and welfare throughout later life. [Evidence Grade: Substantial.]

Recommendation 3:

High THC-content products are generally associated with higher risks of various (acute and chronic) mental and behavioral problem outcomes. Users should know the nature and composition of the cannabis products that they use, and ideally use cannabis products with low THC content. Given the evidence of CBD’s attenuating effects on some THC-related outcomes, it is advisable to use cannabis containing high CBD:THC ratios. [Evidence Grade: Substantial.]

Recommendation 4:

Recent reviews on synthetic cannabinoids indicate markedly more acute and severe adverse health effects from the use of these products (including instances of death). The use of these products should be avoided. [Evidence Grade: Limited.]

Recommendation 5:

Regular inhalation of combusted cannabis adversely affects respiratory health outcomes. While alternative delivery methods come with their own risks, it is generally preferable to avoid routes of administration that involve smoking combusted cannabis material (e.g., by using vaporizers or edibles). Use of edibles eliminates respiratory risks, but the delayed onset of psychoactive effect may result in the use of larger than intended doses and subsequently increased (mainly acute, e.g., from impairment) adverse effects. [Evidence Grade: Substantial.]

Recommendation 6:

Users should avoid practices such as “deep inhalation,” breath-holding, or the Valsalva maneuver to increase psychoactive ingredient absorption when smoking cannabis, as these practices disproportionately increase the intake of toxic material into the pulmonary system. [Evidence Grade: Limited.]

Recommendation 7:

Frequent or intensive (e.g., daily or near-daily) cannabis use is strongly associated with higher risks of experiencing adverse health and social outcomes related to cannabis use. Users should be aware and vigilant to keep their own cannabis use—and that of friends, peers, or fellow users—occasional (e.g., use only on 1 day/week, weekend use only, etc.) at most. [Evidence Grade: Substantial.]

Recommendation 8:

Driving while impaired from cannabis is associated with an increased risk of involvement in motor-vehicle accidents. It is recommended that users categorically refrain from driving (or operating other machinery or mobility devices) for at least 6 hours after using cannabis. This wait time may need to be longer, depending on the user and the properties of the specific cannabis product used. Besides these behavioral recommendations, users are bound by locally applicable legal limits concerning cannabis impairment and driving. The use of both cannabis and alcohol results in multiply increased impairment and risks for driving, and categorically should be avoided. [Evidence Grade: Substantial.]

Recommendation 9:

There are some populations at probable higher risk for cannabis-related adverse effects who should refrain from using cannabis. These include individuals with predisposition for, or a first-degree family history of, psychosis and substance use disorders, as well as pregnant women (primarily to avoid adverse effects on the fetus or newborn). These recommendations, in part, are based on precautionary principles. [Evidence Grade: Substantial.]

Recommendation 10:

While data are sparse, it is likely that the combination of some of the risk behaviors listed above will magnify the risk of adverse outcomes from cannabis use. For example, early-onset use involving frequent use of high-potency cannabis is likely to disproportionately increase the risks of experiencing acute or chronic problems. Preventing these combined high-risk patterns of use should be avoided by the user and a policy focus. [Evidence Grade: Limited.]

Note. A detailed rationale for each evidence grade is provided as a supplement to the online version of this article at


  1. Problem use (DSM-V) is defined by the following diagnostic criteria: (1) tolerance; (2) withdrawal; (3) craving or a strong desire to use; (4) recurrence use resulting in a failure to fulfill major role obligations (work, school, home); (5) Recurrent use in physically hazardous situations (e.g., driving); (6) Use despite social or interpersonal problems caused or exacerbated by use; (7) taking eh substance or engaging in the behavior in larger amounts or over a longer period than intended; (8) attempts to quit or cut down; (9) time spent seeking or recovering from use; (10) interference with life activities; and (11) use despite negative consequences. Cannabis use disorder (CUD) is mild (meet 2 or 3 criteria), moderate (meet 4 or 5 criteria), or severe (meet 6 or more criteria).

  2. Fischer B, Russell C, Sabioni P, van den Brink W, Le Foll B, Hall W, Rehm J, Room R. Lower-Risk Cannabis Use Guidelines: A Comprehensive Update of Evidence and Recommendations. Am J Public Health. 2017 Aug;107(8):1277. doi: Review. PubMed PMID: 28700290.

  3. National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington, DC: The National Academies Press; 2017. doi:

Tomás J. Aragón
Health Officer, City & County of San Francisco; Director, Population Health Division

I exercise legal authority to protect and promote equity and health, and I direct core public health services.


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