Gummies for pain relief? Using cannabis while on prescription drugs risky for seniors

You might want to think twice before giving grandma cannabis gummies for her knee pain.

The popular edible (and cannabis in general) can pose severe medical risks when combined with medications seniors frequently use – including blood thinners, antidepressants and cholesterol drugs. Cannabis products can cause toxic buildup of the medications in the bloodstream, or conversely, reduce their effectiveness.

But you wouldn’t know any of that from the attractive packaging that promotes the products.

Health Canada labeling guidelines require safety warnings that alert consumers to the danger of using cannabis while driving, breastfeeding, pregnant or operating heavy machinery; and use by adolescents. But the labels have no warnings for the seniors – a demographic whose cannabis use has increased seven-fold between 2012 and 2022.

Product labels fail to warn consumers that cannabis can have severe interactions with certain medications, especially those most often used by seniors. For example, CBD products can reduce the activation of blood thinner clopidogrel, increasing the risk of a stroke. And there is no way to predict this.

Seniors are at higher risk of adverse events because they have slower metabolisms and may take multiple medications that can interact with cannabis. An edible that typically takes an hour to kick in may take two hours for a senior, leading them to think it may not be working and take another or a more potent one. This is known as “stacking,” and can result in negative side effects such as dizziness, falls, nausea or drowsiness.

Beatrice May experienced the risks when she first tried medical cannabis at age 82. “I went to put the cannabis honey on my toast, but I accidentally squeezed too much because of the arthritis in my hands,” said May, who lives alone. “I didn’t think anything serious would happen but within 30 minutes I had to call 911 because the room was spinning and had to hold onto the wall until the ambulance arrived.”

May takes warfarin, a blood thinner, for her atrial fibrillation and was unaware that cannabis can elevate levels of the drug, putting her at risk for increased bleeding. May also takes a statin and SSRI that can interact with cannabis and result in elevated concentrations in the bloodstream, increasing side effects such as myalgias (muscle aches), dizziness and nausea.

According to a Canadian Pharmacist Association (CPhA) survey, 61 per cent of medical cannabis users are self-medicating with no medical oversight and 60 per cent are taking cannabis alongside other prescribed medications. However, only 24 per cent of medical cannabis users believe that combining cannabis with other medications can lead to unwanted side effects or drug interaction.

“Seniors have limited options for pain control due to interactions with other medications such as antihypertensives,” says British Columbia pharmacist Stephanie Houston. Meanwhile, “their friends and grandchildren are increasingly introducing them to cannabis for pain relief.”

Cannabis contains substances such as THC, CBN and CBD that have physiological effects on the body. Called cannabinoids, they can interfere with enzymes that help metabolize a wide range of drugs, increasing the levels of the medication in the bloodstream, resulting in stronger side effects or overdose. Conversely, it can increase the rate of metabolism of the drug so it is less effective. CBD interacts with 540 medications, and THC interacts with 400 medications, researchers say.

Canadians spent $4.5 billion on cannabis products from licensed dispensaries last year, up from $153 million in 2018. Licensed retail stores sell cannabis to both recreational and medicinal users – minus health oversight and professional advice. It’s like picking up the serious pain medicine prednisone off the shelves next to lollipops and candies.

“We have already begun to see the consequences of the blurred lines between the recreational and medical cannabis framework (in which) government policies have prioritized the recreational cannabis stream at the expense of patients who use medical cannabis,” says Glen Doucet, CEO of the CPhA.

In 2019, a year after cannabis was decriminalized, the CPhA, representing 43,000 Canadian pharmacists, told Health Canada that it is unsafe to allow medical cannabis in retail stores where sales are not accompanied by oversight and advice from health professionals.

The CPhA recommends that pharmacists be included in the management and distribution of medical cannabis products. Pharmacists can provide expert guidance on dosing, appropriate use, contra-indications, drug interactions, management of side effects, alternative therapies and potential addictive behaviour. A separate protocol should govern recreational retail.

“Patients should refer to drug monographs from their pharmacies to e nsure there are no severe interactions with cannabis and consult with their pharmacist before use,” says Michael Nohra from the Cannabis Branch of Health Canada.

Drug monographs provide directions, safety warnings for interactions with other medications, common supplements, alcohol, green leafy vegetables and even grapefruit. However, in Canada they do not include any information about interactions with cannabis. Patients have to visit Health Canada’s website for that information.

In Canada, [drug monographs] do not include any information about interactions with cannabis.

“Drug monographs do not contain warnings about interactions with cannabis, nor does the e-CPS (e-version of the Compendium of Pharmaceuticals and Specialties), a required reference for pharmacies that [has] almost every drug monograph for drugs sold in Canada,” says Houston. “Given that cannabis has been legal for five years and serious interactions are well established, pharmacies and pharmaceutical companies should include these interactions on drug monographs.”

Christian Ouellet, vice president of corporate affairs with Sandoz, Canada’s first pharmaceutical company to enter the medical cannabis field, says that “Health Canada is the source of guidance for pharmaceutical companies for safety information about cannabis and adverse events.” But “safety warnings could be placed in retail stores to alert consumers about precautions and medication interactions.”

Sandoz teamed up with licensed producer Tilray in 2019, promising more research and education for the public and for health-care providers. It had the intention of distributing medical cannabis products in pharmacies but Canadian laws did not allow for this, so it left the market. No other pharmaceutical company in Canada is producing medical cannabis.

Shoppers Drug Mart got into the medical cannabis industry in 2019, expecting the government would change regulations and allow medical cannabis to be prescribed by pharmacists. The company exited medical cannabis earlier this year because it was unhappy with the current model. It claims that medical cannabis remains the only medication that is not dispensed in pharmacies.

“As we move away from medical cannabis distribution, we remain firm in our belief that this medication should be dispensed in pharmacies like all others and will continue our advocacy to that end,” said Jeff Leger, CEO of Shoppers Drug Mart.


The comments section is closed.

  • Bala Naidoo FRCPC says:

    Concerns regarding CBD advese interactions with medications commonly used by seniors is valid and difficult to anticipate/manage
    Warning labels should be mandatory.

  • Doug Pederson AKA SpectateSwamp says:

    Nope you are wrong
    The father of chinese medicine listed nearlym 100 ailments that responded to Ma Weed Pot Marijuana.
    Traditional cures work. PERIOD

  • Susanne says:

    SERIOUSLY useful information!


Sangeetha Nadarajah


Sangeetha Nadarajah is a U.S. board-certified family physician practicing in Vancouver. She completed her residency training at Southern Illinois University School of Medicine in Quincy, Ill., and has a background in rural, hospitalist and emergency medicine. She has a special interest in lifestyle medicine and myofascial pain. She is passionate about evidence-based yoga research and her upcoming book explores the therapeutic benefits of yoga. Her holistic approach to health care incorporates lifestyle medicine, empowering her patients to achieve overall well-being.

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