Cannabis can cause health problems both physical and mental, including things like anxiety and paranoia.
You can get up to five years in prison for possessing it and 14 years for supplying it.
After alcohol and tobacco, cannabis is the most commonly used drug in the UK.
A small number of people who use cannabis go on to use other drugs. But most people do not, it is claimed.
Cannabis is a naturally occurring drug made from parts of the cannabis plant.
The cannabis plant contains tetrahydrocannabinol (THC) as its main active ingredient. Different forms of cannabis tend to contain different amounts of THC. The higher the amount, the stronger the effects will be.
People use cannabis to relax and chill out. Most people mix it with tobacco and smoke it like a cigarette in a 'joint'. Some people put it in a pipe or 'bong' and smoke it that way. Others make tea with it or bake it in 'hash cakes' or cookies.
Some people use the cannabis plant to help with certain medical problems. But it is still illegal to possess cannabis no matter what it is used for.
With long term or heavy use, smoking cannabis can cause lung disease and possibly cancer, especially as it is often mixed with tobacco.
Regular cannabis use, especially when young, can lead to an increased risk of later developing a psychotic illness.