Pharmacists Assess Risks and Benefits of Medical Marijuana

Marcia Frellick

December 17, 2013

The landscape is rapidly evolving for medical marijuana laws, and the role of pharmacists in serving patients who use it is complex and changing.

Two experts spoke on what pharmacists should know to help their patients during a session at the American Society of Health-System Pharmacists Midyear Clinical Meeting in Orlando, Florida.

Since California first allowed use of medical marijuana in 1996, 19 other states and the District of Columbia have passed laws to allow it. Connecticut's legislature has gone a step further and reclassified marijuana from a schedule I drug, suggesting no medical benefit, to a schedule II drug.

However, because federal law considers marijuana a schedule I drug, doctors are prevented from prescribing it and pharmacies are prevented from dispensing it.

Pharmacists are left to decipher how they can help their patients legally and effectively. They also have to consider that marijuana can have adverse effects when taken in combination with other drugs, said Laura Borgelt, PharmD, associate professor in clinical pharmacy and family medicine at the University of Colorado in Denver. "Anytime you're using a CNS depressant, there can be additive depressant effects, so alcohol, benzodiazepines, antihistamines, and narcotics can cause varied interactions."

Medical marijuana can also adversely affect patients with immunosuppression, psychiatric disturbances, and cardiac and respiratory diseases.

In addition, the adverse effects of medical marijuana in young people, whose brains continue to grow into their 20s, must be considered, said Lawrence Cohen, PharmD, associate dean at the University of North Texas College of Pharmacy in Fort Worth. "By using this at an earlier age, you really could interfere with normal brain development," he said.

Positive interactions can include greater pain relief when used in conjunction with opioids, which could lead to a reduction in use. Patients should be made aware of this, he said.

Large clinical trials are needed to explore the benefits and harms of interactions, both doctors said.

Three Ways to Use It

Dr. Borgelt explained that there are 3 ways marijuana can be used. It can be smoked or the vapor can be inhaled, it can be ingested with food or drink, and it can be absorbed through a topical cream or tincture.

Deciding which form is best has fallen to the patients, she said.

"It's kind of following a self-titration model," she said. Whether that's good or bad is being debated across the country. She noted that if patients are choosing to inhale it, she prefers that they vaporize it instead of smoke it because of the harmful effects of smoking. Eating it can be problematic because it takes longer to feel the effects — possibly several hours — and patients who don't think it's working could ingest another dose, she explained.

Having a pharmacist who can help patients understand the choices and explain that marijuana has grown much more potent over the decades and comes in many different forms is very important, she said.

Pharmacists need to ask the right questions to have those conversations.

"People may be using it as an add-on therapy for things they're already getting, and we need to know," Dr. Cohen said. "You want to make it clear to patients that you want to know about everything they use, not just prescription drugs, but nonprescription drugs and even herbal supplements. There may be interactions that can be clinically significant."

American Society of Health-System Pharmacists (ASHP) Midyear Clinical Meeting. Presented December 10, 2013.

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