Since the 1950's many people have found success with DR. A.T.W. Simeons' HCG diet, a man who had studied obesity in Europe for 40 years. Even still, HCG has been raising eyebrows for its entire existence, though it's sustainability through the years can be interpreted as a success for the diet. 

HCG, or human chorionic gonadotropin, a key component in Dr. Simeons' rapid weight loss plan, is actually a hormone that supports the normal development of an egg during ovulation. It is extracted from the urine of pregnant women and used for a variety of conditions, including to treat infertility in women and increase male sperm count, as well as to address latent puberty in adolescent makes. In the HCG diet protocol, which consists of an extreme low-calorie diet plus injections, HCG is said to attenuate unrelenting hunger pangs, feelings of fatigue, headaches and sarcopenia or muscle wasting that can sometimes accompany extreme diets, providing for better results.

HCG improves fertility by increasing sperm production in men and encouraging egg release in women. It also helps treat sex hormone-linked conditions, such as undescended testes in young men and undeveloped sexual traits in girls. Depending on its use, HCG is considered to be either an endocrine drug or a fertility drug. The Food and Drug Administration (FDA) first approved HCG in 1974.

Doctors don't consider HCG to be safe if you:

Are pregnant

Are allergic to HCG or any other ingredient found in the drug

Are an "early bloomer," entering puberty sooner than normal

Have prostate cancer or another cancer that is stimulated by male hormones, or androgens.

Before taking HCG, tell your doctor if you:

Have any allergies

Have heart disease

Have kidney disease

Have an ovarian cyst

Suffer from seizures

Have migraines

Have asthma

Are in early puberty

HCG Interactions

Tell your doctor all the medications you're taking.

This also includes prescription and over-the-counter medications, vitamins and other dietary supplements (nutritional shakes, protein powders, etc.), herbal remedies and any illegal and recreational drugs.

Ask your doctor or pharmacist about HCG if you're taking any medications that affect your blood. This includes:

Drugs for clotting disorders like coagulation factors IX and VIIa

Drugs that increase red blood cell production like epoetin alfa (Epogen, Procrit), factor VIII concentrate (Humate-P ), and darbepoetin (Aransep )

Cancer drugs affecting blood supply like bevacizumab ( Avastin), lenalidomide (Revlimid), and thalidomide ( Thalidomid)

tretinoin (Atralin, Avita, Renova, Retin-A )

There is also the risk of side effects when taking HCG: 

Common Side effects of HCG

Headache

Irritability

Restlessness

Fatigue

Depression

Swelling in the feet, ankles, lowers legs, or hands

Appearance of female breasts in men

Pain in the area where you received the injection

Serious Side Effects of HCG

Entering puberty sooner than normal

Painful rupture or swelling of the ovaries

Allergic reactions, including life-threatening ones

Blood clots

Multiple pregnancies (conceiving twins or triplets)

So, when taking HCG, make sure to consult your physician regarding any potential side effects as to remain safe while on the diet.