Doctors looking to harness the benefits of cannabis may do better to focus on boosting the body's own pain relief system, scientists suggest.
Cannabis extracts are hard to target
The human body has its own endocannabinoid system which helps regulate pain, hunger and anxiety.
Experts at the Federation of European Neuroscience Societies meeting in Vienna said using plant cannabinoids would mean less targeted therapies.
They said this meant it was harder to avoid unwanted side-effects.
Experts said this was because it was the drug affected many different areas in the brain, nerves and immune system.
Research was presented to the conference which showed that a cannabis-like chemical, could worsen symptoms in mice with an epilepsy-like condition.
However, doctors stress previous studies in animals and humans have shown that multiple sclerosis patients can benefit from cannabinoid medicines.
Professor David Baker, of the Institute of Neurology at University College London, who attended the meeting, said: "There is a benefit of moving from agents from illegal plant based medicines to looking at how we use pharmaceutical medications to target the benefits of cannabinoids, but reduce the well known adverse effects."
The only cannabis-based drug which can be currently be used in the UK is a treatment for MS called Sativex.
It has been granted a special licence meaning it can only be used if the doctor takes responsibility for prescribing it.
The drug, produced by GW Pharmaceuticals, is a mouth spray containing two chemicals found in cannabis, THC and cannabidiol.
It is made using plant cannabinoids.