This was on NHS site
What about products available to buy?
Some cannabis-based products are available to buy over the internet without a prescription.
It's likely most of these products – even those called "CBD oils" – will be illegal to possess or supply. There's a good chance they will contain THC, and may not be safe to use.
Health stores sell certain types of "pure CBD". However, there's no guarantee these products will be of good quality.
They tend to only contain very small amounts of CBD, so it's not clear what effect they would have.
Is medical cannabis safe?
The risks of using cannabis products containing THC (the chemical that gets you high) are not currently clear. That's why clinical trials are needed before they can be used.
"Pure" products that only contain CBD, such as Epidyolex, do not carry these unknown risks linked with THC.
But in reality, most products will contain a certain amount of THC.
The main risks of THC cannabis products are:
psychosis – there is evidence that regular cannabis use increases your risk of developing a psychotic illness such as schizophrenia
dependency on the medicine – although scientists believe this risk is probably small when its use is controlled and monitored by a specialist doctor
Generally, the more THC the product contains, the greater these risks are.
Cannabis bought illegally off the street, where the quality, ingredients and strength are not known, is the most dangerous form to use.