The scientists from the California Pacific Medical Center Research Institute (CPMCRI) believe their discovery may provide a non-toxic alternative to chemotherapy and achieve the same results minus the painful and unpleasant side effects.

The research team say that cannabidiol or CBD, unlike cannabis, does not have any psychoactive properties so its use would not violate laws, but they are not suggesting patients smoke marijuana.

The scientists say it is highly unlikely that effective concentrations of CBD could be reached by smoking cannabis.

According to lead researcher Dr. Sean McAllister, CBD works by blocking the activity of a gene called Id-1 which is believed to be responsible for a process called metastasis, which is the aggressive spread of cancer cells away from the original tumour site.

Earlier research has also shown CBD can block aggressive human brain cancers and this latest study has found that CBD appears to have a similar effect on breast cancer cells.

Dr. McAllister says there are currently a limited range of options for treating aggressive forms of cancer and while treatments, such as chemotherapy, can be effective they can also be extremely toxic and tough for patients.

McAllister says CBD offers the hope of a non-toxic therapy that could achieve the same results without any of the painful side effects but experts say the research is at a very early stage.

Cancer UK says the laboratory findings will need to be followed up with clinical trials in humans in order to establish if the compound is safe, and whether the beneficial effects can be replicated.

Cancer experts say there already exist several cancer drugs which are based on plant chemicals such as vincristine, derived from a flower called Madagascar Periwinkle which is used to treat breast and lung cancer.

They say any drug that has fewer side-effects than chemotherapy will be of great interest.

The study is published in the journal Molecular Cancer Therapeutics.

Parkinson's disease affects millions of people worldwide; symptoms, such as tremors, difficulty in moving and muscles that tighten and lock, usually appear when a person is over 50.

There is no cure for the disease and while several drugs are available to treat symptoms, some patients experience side-effects, among them a condition called dopamine dysregulation syndrome.

Patients affected by this effect need increasing doses of medication and become prone to aggressive outbursts and indulge in risky behaviour.

Parkinson's disease is caused by a loss of nerve cells in one part of the brain where the cells release a chemical called dopamine; this allows messages to be sent to parts of the brain that coordinate movement and as the dopamine-producing cells die off, these parts of the brain stop functioning properly.

Along with this levels of another chemical messenger, which dampen down over-active cells, also begin to drop and it is these chemical levels which were boosted in the trial.

The team are now planning a second, larger trial of the therapy, due to begin early next year which is expected to last 18 months.

The study is published in the current issue of the journal Proceedings of the National Academy of Sciences.