Advocates say cannabis could be a source of treatments
A large scale study in the US and Canada, compared the two after suggestions drugs derived from cannabis could boost appetite.
Researchers from the Mayo Clinic in Rochester, Minnesota and the North Central Cancer Treatment Group said their finding to the contrary should "dampen enthusiasm" for using cannabis medications in this way.
The study monitored 469 cancer patients aged 18 and over between December 1996 and December 1999.
All had reported some loss of appetite or weight loss of at least five pounds during the preceding two months.
Search for answers
Doctors compared the effects of megestrol acetate, a standard drug for treating loss of appetite and weight in cancer patients, with dronabinol (Marinol), which is derived from marijuana.
Some patients were given both drugs.
Of those taking only the standard treatment, 75% said their appetite improved, compared to just 49% of patients taking dronabinol.
And 11% of those on megestrol acetate, gained more than 10% of their baseline weight, compared with only 3% who were taking dronabinol.
The study also found that there was no notable benefit when both drugs were given together.
Dr Aminah Jatoi, who led the research, said: "These findings should dampen enthusiasm for using marijuana derivatives for this purpose.
She added: "Nobody knows all of the factors that come into play as cancer patients lose weight.
"This study was an attempt to help cancer patients by finding some answers about what works and what doesn't work for those struggling with eating.
"To our knowledge, this is the first study to compare a standard drug to a drug derived from marijuana in an effort to help cancer patients with this problem."
She said megestrol acetate was not the complete answer, and more work needed to be done to find better drugs.
But she said it was more effective than the cannabis derivative.
GW Pharmaceuticals is spearheading UK research into the medicinal benefits of cannabis, concentrating on its pain relieving effects, rather than appetite or weight gain.
Mark Rogerson of GW Pharmaceuticals said: "As the US researchers have noted, there is anecdotal evidence linking the recreational use of cannabis to appetite stimulus.
"We have found that patient response to cannabis medicine tends to be very dose-specific, and it may be that these results hold only for the doses tested.
"We note that appetite gain was observed in nearly 50% of cases, and would regard that as a welcome adjunct to the pain relief which we believe can be provided to cancer patients by a cannabis medicine."
The results of the study are published in the Journal of Clinical Oncology.