Medicinal Cannabis

August 20, 2009

Adverse Effects, Preparation, Dosing, Contraindications

In the Summer 2009 edition of  O’Shaughnessy’s, the Journal of Cannabis in Clinical Practice, edited by Fred Gardner,  is a review by Frank Lucido, MD, of a book that I have ordered.  I just need to time to read.

Marijuana Medical Handbook by Dale Gieringer PhD, Ed Rosenthal, and Gregory T. Carter MD; Quick American, Oakland, 2008; 257 pages (paperback); $19.95

I found the review to be very helpful and want to simply mention a small section of it below.

But first, and NOT in the review, though perhaps it is in the book, it is difficult to find mention of contraindications in the literature. I list them here.



Ischemic heart disease or low blood pressure are contraindications to use. Cannabis may lower blood pressure 10 or 20 points and increase heart rate as much as 50 to 60 points according to one protocol that tested it for postoperative pain. This is dose related. If your blood pressure is already as low as 100 or 105, it may drop your blood pressure too low for safe use.

One patient on a higher dose developed a profound vasovagal reaction with severe slowing of the heart rate and blood pressure that ended the study. Again, that is dose related.

Immunosuppressed patients may be wise to avoid smoking it or risk infection with Aspergillus which is a fungus that may affect lungs or sinuses.  The spores are in the air; using filters in growing rooms should prevent it from growing. Large collectives may use forensic microscopes to examine their harvest and they avoid package in cellophane which can cause formaldehyde to form.

To avoid risk of Aspergillus, you may use cannabis under your tongue, swallow it or use it topically in an ointment.


Returning now to advice from the book and review by Dr. Frank Lucido:

Adverse Effects

Providing the pros and cons, as any good clinician should, the authors devote a chapter to “real and imaginary” side effects. Allergic reactions, though rare, are real and can manifest as rapid heartbeat, faintness/fainting, twitches, numbness, headaches and rashes. “If you regularly experience discomforting reactions from marijuana, the best treatment is to avoid it,” the authors wisely advise.


Preparation and Dosage Methods

Delivery systems available to medical marijuana users include smoking, vaporization, tinctures, edibles, and topicals. Edibles typically take 45-60 minutes to come on, but their effects can last six to eight hours. One question frequently asked by patients who are new to using marijuana as medicine concerns the difference between smoking and ingesting via edibles. The handbook explains: “Anything absorbed through the stomach is processed by the liver before it reaches the brain. In the liver, THC is converted to 11-hydroxy-THC, a metabolite that is if anything more psychoactive than ordinary THC. Because 11-hydroxy-THC is not produced when marijuana is smoked, eating and smoking produce different pharmacological effects. “Some people regulate their conditons by eating small amounts of marijuana on a regular basis, sometimes just once or twice a day. They barely feel any effect from the drug except for the relief of their symptoms.

“The major drawback of ingesting marijuana is that the effective dose can be difficult to predict.”

The review is excellent and I need this book.


For my own patients with complex medical conditions, I recommend they pay attention to the details in the last section.  I am advising that they avoid swallowing the drug, and consider the potential interactions with multiple medications they use for their medical conditions. Once Sativex is available, or once clones with CBD content become available, there will be fewer psychotropic side effects such as euphoria. I refer you to O’Shaughnessy’s for Fred Gardner’s exciting report 3-31-09 on cannabidiol (CBD).  “CBD is the nonpsychoactive cannabis constituent that is “an oral anti-arthritic therapeutic in murine collagen-induced arthritis.” See also research mentioned on this blog by GW Pharmaceuticals that has found it to be more easily tolerated and more effective than THC for neuropathic pain, for spasticity of Multiple Sclerosis, and other conditions. GW Pharmaceuticals’ product Sativex is a 50:50 mixture of THC and CBD, which they are bringing to market. It is an oral spray now used in 20 countries.


Pharmacokinetics:  In a 2003 review by Franjo Grotenhermen, onset of effect varies with route used. Higher bioavailability may be obtained in an oral matrix such as sesame oil. Absorption may be 95% in an oil vehicle, and still as high as 90 to 95 % in a water based cherry vehicle. But ingesting THC 20 mg in a chocolate cookie or dronabinol 10 mg results in very low bioavailability of 6% to 7% with a range of 2% to 14%, and high inter-individual variation.

With oral ingestion, absorption is slow and erratic, onset of effect may be delayed 30 to 90 or even 120 minutes, reach a peak in 2 to 3 hours or even 6 hours in some cases —  “Several subjects showed more than one plasma peak” — and last 4 to 12 hours depending on dose. In the meantime, you may have eaten much more, and it may be too late to discover 6 hours later that you have overdosed.  When it is eaten, the effect is longer. I fear the first time you try ingesting it, you may use too much. Who doesn’t love brownies?

With inhalation, the maximum plasma concentration occurs in minutes, effects start in seconds to minutes, reach maximum after 15 to 30 minutes and taper off in 2 to 3 hours.

Using a liquid form under the tongue is likely to be similar to inhalation with the rate of onset and duration of effect, i.e. faster onset and shorter duration depending upon the dose.

If you are new to using it, then start with a low dose and increase slowly. Avoid ingesting brownies or cookies or tea until you have established a comfort zone with your use and get a sense of how your system is responding to that mixture. Watch for the psychotropic side effects that are worse when ingesting the drug.

If you are working with a psychiatrist or psychologist for panic attacks and depression, it would be helpful to include that specialist in your plans and limit your dose until you are comfortable with use. It may relieve depression and anxiety, give a sense of relaxation and well being, but overdose may cause panic, with rapid pulse and lower blood pressure.


Heavy regular use may lead to dependency  – being dependent is not the same as being addicted – and withdrawal may cause side effects lasting 10 to 14 days in some, but it is not as severe as from opioids or alcohol.


Acute overdose may result in panic attacks or anxiety, rapid heart rate, low blood pressure. So the rule is to start a low dose and go slowly. This is not a race.



The material on this site is for informational purposes only, and

is not a substitute for medical advice, diagnosis or treatment provided by a qualified health care provider.




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