The basic principle for dosing medical marijuana is to start with a low dose and to go slow in taking more until the effect of the first dose is fully realized, because the effects of cannabis are not always immediately felt. Starting low and going slow allows patients to accommodate for the different experiences they may have.

Cannabis has a wide margin of safety and there is limited risk of overdose. However, caution is warranted until a patient fully understands the effect that the cannabis may have. Dosage varies greatly among patients, even when treating the same condition.

The effect of medical marijuana is affected by several factors some of which are:

  • Amount used (dosage)
  • Strain used and method of consumption
  • Environment/setting
  • Experience and history of cannabis use
  • Mindset or mood
  • Nutrition or diet and
  • Mode of administration

Modes of administration of medical marijuana


Inhalation has the primary advantage of allowing a patient to adjust the dosage easily for maximum benefit because the onset of action is almost immediate. The medical marijuana is taken into the lungs and quickly absorbed through the capillaries into the bloodstream.

Forms of inhalation

  • Hand or machine rolled cigarette (joint)
  • Pipe or water pipe (bong)
  • Vapour Inhalation

Length of effect

Effects from inhaling cannabis products are felt within minutes and reach their peak in 10–30 minutes. Typical inhalers experience an effect that tapers off after approximately 2–4 hours, and lasts about 4–12 hours. As cannabis affects your cognitive abilities, you should not operate a motor vehicle, operate heavy machinery, or engage in any activity that requires full cognitive abilities until after the effect of the cannabis has completely dissipated, no less than 24 hours after use.

Smoking versus Vaporization

Smoking involves combusting the cannabis using an open flame. Vaporization steadily heats the cannabis to a temperature high enough to extract THC, CBD, and other cannabinoids into an inhalable mist, without burning.

Differences between smoking and vaporization

  • With smoking, up to 40% of the available cannabinoids may be completely combusted or lost in side-stream smoke and thus are biologically unavailable.
  • A vaporizer steadily heats dried cannabis to a temperature that is high enough to extract THC, CBD, and other cannabinoids but too low to release the potentially harmful toxins that occur during combustion.
  • Vaporization is claimed to reduce some of the health risks associated with smoking.
  • There may be differing vaporization points for the individual cannabinoids and vaporized cannabis may have differing concentrations and ratios of cannabinoids compared with smoked cannabis

Oral Administration

Many patients are more comfortable with oral administration of medical marijuana. Patients should consider, however, that absorption is slower when medical marijuana is taken orally, with lower, more delayed peak THC levels and reduced bioavailability of THC and CBD due to extensive metabolism in the digestive tract.

Effects of Medical Marijuana

Short-Term Cognitive Effects

Patients should be aware that cannabis use causes short-term impairments in the following brain functions:

  • Memory
  • Sense of time
  • Sensory perception
  • Attention span
  • Problem solving
  • Verbal fluency
  • Reaction time
  • Psychomotor control

Cannabis users may “pull themselves together” to concentrate on simple tasks for brief periods of time. That said, performance impairments may be observed for at least one to two hours following cannabis use, and residual effects have been reported up to 24 hours depending on potency of the cannabis, the method of administration, and the tolerance of the user.

Long-Term Cognitive Effects

Consult the advice of your physician if you are a long-term user of medical cannabis and intend to stop using it, or if you are concerned about dependence on or addiction to cannabis. Your physician can help you manage any withdrawal effects that you may experience. Always seek the advice of your physician or other qualified healthcare provider before starting any new treatment or discontinuing an existing treatment with medical cannabis.