Safety
Toxicity
Medicinal cannabis products are generally regarded as having low acute toxicity. However, concurrent use of other drugs may mask the effects of cannabis and severe toxicity including adverse cardiovascular effects and death may be under-recognised.
In mammals, the median lethal dose of THC has been estimated to be >800mg/kg. CBD appears to be of very low toxicity. Doses of 1000mg/kg CBD appear to have been tolerated safely in humans.
Dependence Potential
The following table outlines the safety ratio of cannabis in comparison to other drugs commonly used for pain treatment:
| Substance | Effective Dose (ED) | Lethal Dose (LD) | Safety Ratio (LD/ED) | Dependence Potential |
|---|---|---|---|---|
| Cannabis – THC (sm) | 15mg | >15g | 1000 | Low / Moderate |
| Codeine (or) | 40mg | 800mg | 20 | Moderate / High |
| Morphine (or) | 20mg | 300mg | 15 | High |
| Alcohol Ethanol (or) | 33g | 330g | 10 | Moderate |
(or = oral ingestion, sm = smoking)
We may need a reference here and a disclaimer.
Absorption
As cannabinoids are highly lipophilic, they are quickly absorbed and distributed into body fat. The resultant concentrations in the blood following oromucosal administration are lower than those obtained by inhaling the same dose of THC because absorption is slower and redistribution into fatty tissues is rapid.
THC and CBD are metabolised in the liver, and approximately one third of the parent drugs and their metabolites are excreted in the urine (the remainder via the faeces). THC and CBD may be stored for as long as four weeks in the fatty tissues from which they are slowly released at sub-therapeutic levels back into the blood stream, then metabolised and excreted via the urine and faeces.
Side effects (adverse drug reaction)
Medicinal cannabis, like any medicine, may have side effects for some individuals. In the case of medicinal cannabis, most of the commonly reported side effects are minor and temporary. The most commonly reported side effect when taking medicinal cannabis products is mild or moderate dizziness and disorientation. For most people, this is most frequent in the first few weeks of treatment. Since CBD is minimally psychoactive, individuals taking CBD only medicinal cannabis products are likely to experience fewer side effects than those taking formulas that contain THC.
Side effects of medicinal cannabis may include:
Less serious side effects
Very common
(affecting more than 1 in 10 people):
- feeling dizzy or tired
- feeling or being nauseous
- diarrhoea
- eating more or less than usual
Common
(affecting less than 1 in 10 people):
- problems with your memory or having trouble concentrating
- feeling irritable
- behaviour getting worse
- difficulty speaking
- lack of energy or feeling weak or generally unwell
- feeling abnormal or drunk
- loss of balance or falling over
- blurred vision
- changed sense of taste or a dry mouth
- constipation
- stomach pain
- headache
Uncommon
(affecting less than 1 in 100 people)
- fainting
- changes in pulse rate, heart rate or blood pressure
Although serious side effects are rare, some individuals may experience more serious side effects when taking THC-containing medicinal cannabis products, including:
Serious side effects
Very common
(affecting more than 1 in 10 people):
- seeing or hearing things that are not there (hallucinations)
- believing ideas that are not true
- feeling that other people are against you
- thoughts of suicide
- feeling depressed or confused
- feeling over-excited or losing touch with reality
- worsening fits or seizures related to epilepsy
Contraindications
Medicinal cannabis is contraindicated in patients who:
- have hypersensitivity to cannabinoids or to any of the excipients
- have a personal or family history of serious psychiatric disorders (particularly schizophrenia)
- who have unstable cardiovascular disease
- who are pregnant, planning on becoming pregnant or are breastfeeding
Reporting adverse reactions
Reporting adverse reactions is important. It allows continued monitoring of the benefit-risk balance of the medicinal product. Healthcare professionals and patients are encouraged to report any suspected adverse reactions at www.tga.gov.au/reporting-problems.