Synthetic cannabis may slow the growth of bowel cancer, a new study suggests.

Researchers at Pennsylvania State University tested several synthetic and natural compounds derived from the plant against the cancer cells.

While natural cannabis had little effect on the disease cells, 10 different synthetic compounds that all worked to slow the growth of tumor cells.

The study is far from proof that marijuana cures cancer, but it may suggest that some cannabis-related compounds might be useful in developing new treatments for colorectal cancer, rates of which are rising, particularly among young Americans.

Cancer treatment often winds up at the center of the controversy swirling around medical marijuana.

Ten compounds made to resemble the structures of cannabinoids slowed the growth of colorectal tumor cells in petri dishes, a new Pennsylvania State University study reveals

Cannabis is legal for medical use in 33 US states and for recreational use in 10.

But because it remains federally criminalized, the Food and Drug Administration does not regulate marijuana sold in those states.

And sellers take advantage of that, advertising their CBD and THC products for everything from stress relief to nausea, pain to, in some places, 'curing cancer.'

Promises like the latter, however, have (rightly) drawn criticism from doctors who worry marijuana is becoming the new snake oil.

So far, there are are only a few clearly proven medical uses for marijuana.

There is an FDA-approved CBD product that treats seizures, and a cannabis (including the both CBD and THC, the psychoactive component of marijuana) drug approved to treat chemo-related nausea.

But there has been little evidence that marijuana fights cancer itself.

The new Penn State study suggests that marijuana itself doesn't do much to fight cancer, synthetic cannabinoids just might.

To be clear, these compounds are not cannabis or even derived from it. They are made in the lab to mimic the structure of the drug in order to help scientists study marijuana without having to jump through the considerable regulatory loopholes to get the real thing from the National Institutes of Health.

Some prior research has examined the possible tumor-growth-inhibiting effects of cannabinoids on a variety of forms of cancer.

Colorectal cancer's particular characteristics make it an especially promising target for potential cannabinoid treatment.

It's a fairly well-documented and -researched phenomenon at this point that two cannabinoid receptors are involved in colon and rectal cancer.

Our bodies have an endocannabinoid system - a series of receptors to the shape of the compounds - which is part of the central nervous system.

This receptor network is involved in maintaining a healthy, stable digestive system, which of course includes the colon and rectum.

It seems that when one of these, CB1 is 'turned on' it helps to prevent colorectal tumors from growing. When the receptor is missing or turned off, it promotes the growth of tumors in the organs.

When the other receptor, CB2 is turned on, it seems to have the opposite effect, promoting tumor growth in the colon.

So, the researchers decided to test how they could introduce cannabinoids to alter the behavior and mutations of these tumor cells.

From a library of 370 synthetic compounds (there are an estimated total 480 compounds in cannabis, 66 of which are cannabinoids) Penn State team found 10 that worked to slow the growth of colorectal tumor cells in petri dishes.

'Now that we've identified the compounds that we think have this activity, we can take these compounds and start trying to alter them to make them more potent against cancer cells,' study co-author and pharmacology department chair Dr Kent Vrana said.

'And then eventually, we can explore the potential for using these compounds to develop drugs for treating cancer.'

The researchers divided the synthetic cannabinoids into three different groups based on how they seemed to fight tumor growth.

'We know how one of them works, which is by inhibiting the division of cells in general. We also found that the most potent and effective compounds don't seem to work through traditional marijuana receptors, although we're not sure of the exact mechanism yet,' said Dr Vrana.

Compounds that target fast cell division might be particularly important to treating colon cancer because, like the skin, healthy colon cells divide rapidly any way, and that makes them particularly at risk for cancer.

'Every time a cell divides, there's the chance that it will mutate and keep dividing when it shouldn't, which is how cancers can start,' Dr Vrana said.

'So if we block that signal that's telling cancer cells to continue to divide,' as synthetic cannabinoids show promise for doing 'that could be a way to stop that cancer.'

Dr Vrana and his team still need to work out the exact mechanisms at play in the cancer-blocking effects of the compounds, so the research is in its very early stages.

But the findings suggest that these 10 compounds - which are not THC or CBD - may slow or even stop colon cancer growth.