If i am only 20 pounds overweight, is it unhealthy to try the hcg diet for one cycle?

Yes: The HCG diet was originally developed by a.T.W. Simeons M.D. During the 1940's -1950's. It has been used all over the world for over 50 years. This method is extremely safe & effective when used under the care of an experienced & trained md. Apparently HCG has an effect on your hypothalamus, increasing adiponectin levels & reducing leptin resistance. The method must be followed strictly to work.

Placebo: When studied against placebo, the diet did no better than the control group. Given it is a 500 calorie diet, you will likely lose weight but the "hcg" (it is often a unregulated nutraceutical) is not the cause, the calorie restriction. I recommend searching scholar.Google.Com or pubmed and reading yourself.