Start low, go slow: onset and the two-hour rule
What public-health bodies say about how long edible cannabis takes to work and how long it lasts, and why waiting matters.
The two public-health figures
Health Canada's consumer guidance for edible cannabis suggests starting with 2.5 mg of THC or less and going slowly. The same guidance describes onset between 30 minutes and 2 hours, up to 4 hours to full effect and effects that can last up to 12 hours. The US CDC also gives 30 minutes to 2 hours for edibles to take effect.
| Source | Onset | Full effect | Duration |
|---|---|---|---|
| Health Canada | 30 min – 2 h | up to 4 h | up to 12 h |
| US CDC | 30 min – 2 h | — | longer than smoking or vaping |
Why the two-hour wait
Two hours covers the upper end of the typical onset window. Taking more before the first portion has arrived is the most common mistake. If nothing has happened, stop for the day and talk to your health professional about what to do next.
Things that change timing
- Food in the stomach.
- Alcohol, which raises THC levels and impairment; do not combine them.
- Regular use and body weight.
Safety
Do not drive. If someone has chest pain, cannot be roused or is very distressed, call emergency services. This is general information and not medical advice.
- Health Canada, what you need to know if you choose to consume cannabis, canada.ca.
- US CDC, Cannabis and poisoning, cdc.gov/cannabis/health-effects/poisoning.html.
