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Cannabis, Capacity and Consent

Posted May 6th, 2019 in the wire, 2019, thought leadership

by Julian Perez, Vice President of Risk Management & Compliance at dentalcorp

Ever since the government began seriously discussing legalization of marijuana for recreational use, dental professionals have developed an intense curiosity about what the change would mean, both for the health of patients and the provision of care. There are copious studies that explore the potential interactions of common sedatives and anesthetics with cannabis, as well as myriads more that detail how the effects of smoke and THC alter the oral environment. This article explores some of the thornier issues that have arisen from legal and risk management perspectives. Specifically, how cannabis impacts (or doesn’t impact) a person’s capacity to consent to treatment and, secondly, how a patient’s recent marijuana use affects the task of obtaining informed consent to treatment.

At the outset, it’s worth mentioning that dentists have long held a duty to explore medical histories with patients and this long-standing professional obligation includes asking about, among other things, alcohol and drug use. A significant portion of the Canadian population has used cannabis products for several generations; therefore, legal or not, dentists have had a professional obligation to understand the drug’s effects on oral health as well as its interactions with medications administered during dental treatment. Indeed, a recent Statistics Canada report observed that legalizing cannabis doesn’t seem to have significantly changed how many people use the drug.

Notwithstanding that legalization has caused so much ado about nothing, the prospect of patients arriving to their appointments under the influence has sparked an important conversation around mental capacity. Unfortunately, much of the literature pertaining to marijuana’s effects on patients’ capacity to consent is confusing, contradictory and in some cases, just plain wrong.

Capacity to consent

Generally speaking, it is safe to assume capacity. However, when there are signs that psychiatric illness, trauma, sedation, senility or intoxication may be impairing a patient’s mental abilities, dentists will have to determine whether the patient retains the capacity to consent to treatment. To be clear, the use of marijuana (or any other drug) by itself does not automatically result in a finding of incapacity; rather, in such cases an assessment of capacity is required.

Capacity is only one element in informed consent

Establishing capacity is only one aspect in obtaining informed consent to treatment. Consent must also be informed; be provided voluntarily; refer to the treatment administered as well as the clinician who provides the treatment.

For consent to be informed, the clinician must answer any questions the patient has about the treatment and, at a minimum, ensure the patient understands the risks, benefits and reasonable alternatives to treatment (i.e. the material information).

The test for capacity

There is a two-part legal test for mental capacity that every health care provider should know and understand.  While the exact wording may vary from jurisdiction to jurisdiction, essentially the test is that the patient must be able to understand the nature and purpose of the proposed treatment and appreciate the reasonably foreseeable consequences of giving or withholding consent. Note that it is only necessary that the patient be able to understand the treatment—the test is not that he or she actually understands the treatment. That said, making sure the patient understands the treatment is required to fulfill a health practitioner’s regulatory and common law obligations.

It’s important to avoid conflating capacity to consent and informed consent itself.  If actual understanding were the test for capacity, people with low health literacy would too often be incapable of providing consent, as would many patients of clinicians possessing poor communication skills. Where a clinician determines that a patient has capacity to consent but does not adequately understand the nature of the treatment or its consequences, further communication will be required.

Assessing capacity

When assessing capacity, the clinician should explore the patient’s interest in the treatment, whether the patient understands the expected benefits and possible risks, as well as his or her appreciation of the alternatives to treatment. Although the patient’s medical history and current overall state of health may be relevant, the clinician will need to engage the patient in a dialogue to elicit information from the patient and try to gain an understanding of the patient’s state of mind.  

There are several communication techniques which may assist in the assessment process. One of the most useful ways to assess the patient’s ability to understand is called the “teach back technique”. It’s called “teach back” because the clinician asks the patient to repeat back in his or her own words what was said about the condition and its proposed treatment. Using open-ended questions is also important. For example, the clinician may prompt the patient to describe his or her medical condition, proposed treatment and the likely outcome. At the end of this assessment, it is quite possible to determine that a patient is capable of consenting but does not in fact understand the treatment. Think of a patient-clinician pair with a serious language barrier, for example.

Capacity is treatment specific

As noted above, capacity is specific to the proposed treatment. This means that in practice, a patient may be capable of consenting to routine and familiar treatments, but incapable of consenting to irreversible and highly-invasive treatments. This makes sense considering the wide range of treatments provided in a dental office. A patient who is under the influence of drugs (such as marijuana), may be capable of consenting to a hygiene appointment or the insertion of a nightguard, but simultaneously incapable of consenting to full mouth clearance under general anesthesia, with immediate implant placement. Because the test depends on the patient’s ability to understand the nature of the proposed treatment, the more complex the treatment, the greater the mental ability required.

Capacity is fluid and changes over time

It is quite possible for a patient to have, lose, and regain capacity to consent over a short period of time. In the case of cannabis, a patient may be incapable in the morning and perfectly capable by 5:00pm. The moment that matters, legally speaking, is when consent to treatment is provided. Again, this makes sense–patients often provide consent to being treated under sedation but become incapable of consenting before the treatment begins. With respect to consent, therefore, it doesn’t matter if the patient is capable at the time of treatment—what matters is whether the patient was capable when he or she consented. That said, if a patient attends an appointment unexpectedly lacking mental capacity—it is best to reschedule the appointment unless there is a true emergency requiring urgent dental care.

Some procedures may be riskier if a patient has used marijuana

Simply because some risks may be increased due to marijuana use does not immediately lead to the conclusion that a patient is incapable of providing consent. Nor does it mean that a patient’s consent is invalid.  Patients have a right to consent to some risks and certainly to be active participants in their own health care.  That said, just because a patient consents to a treatment does not mean a dentist should automatically provide it.

The Alberta Dental Association and College’s Code of Ethics is instructive: “Dental treatment shall expressly be intended to not leave the patient in a worse state than if no treatment had been provided.” Where a patient requests treatment that appears likely to leave the patient worse off, “a dentist has a right to refuse to provide treatment … even when requested to do so by the patient.” These two statements reflect the principles of beneficence and non-maleficence that are universal to health care. 

Where the rubber meets the road: My patient has shown up high for surgery, now what?

If a patient shows up to an appointment under the influence of cannabis with elevated blood pressure and tachycardia, the risks of treatment may be greatly increased. Bear in mind, it is quite possible the patient is capable of consenting to treatment and/or that a previous consent remains valid.

Whether to go forward with the treatment, however, will depend on the clinician’s professional judgment of the risks to the patient’s well-being of proceeding with versus postponing the procedure(s). If the care is not urgent, the dentist should seriously consider postponing treatment until it is safer to administer.  Conversely, if the risks of postponing the treatment outweigh the risks of proceeding, the fact that the patient has recently used marijuana should not prevent necessary and urgent dental care from taking place.

What if I’m second-guessed: How do I defend my decisions?

Good recordkeeping is the key to defending yourself from a complaint or lawsuit should things not go according to plan. Comprehensive medical histories, accurate and detailed chart notes, procedure-specific consent forms that highlight the most relevant risks, and meticulous documentation of all conversations relating to the assessment of capacity are a dentist’s best defenses against anyone who might later question his or her actions.


Whether a patient who is under the influence of cannabis has capacity depends not on the dosage, mode of administration or timing of marijuana use, but rather on the patient’s ability, at a given point in time, to comprehend the nature of a proposed course of treatment, the purpose of that treatment as well as the consequences of undergoing or refusing the treatment. If a patient smells of marijuana or reports recent use, this is the beginning—not the end—of capacity assessment. Further exploration will be necessary with the goal of establishing the patient’s current cognitive abilities vis-a-vi the treatment at issue. 

Regardless of whether a patient is capable of consenting or does in fact consent, a dentist still has a duty to determine whether proceeding with a specific treatment is advisable given the physiological effects of marijuana on the patient or the potential for dangerous adverse reactions.  A dentist has a right to refuse to provide treatment; however, he or she must also consider the potential risks of delaying urgent care.

As previously published in Oral Health Office's May issue. This can also be found online here

About The Author

Julian Perez has a robust legal background having worked for a Wall Street law firm in Manhattan as well as a professional liability program providing malpractice defense to over 10,000 dentists. In his current role as Vice President of Compliance & Risk Management at dentalcorp, Julian is responsible for the development, implementation, and oversight of company-wide standards, programs, and systems to support practices in the delivery of optimal patient care. Julian holds a Bachelor degree from Yale University and a juris doctorate from Columbia University’s School of Law.

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