Critics of the HCG diet cite a number of side effects attributed to various aspects of the plan. Side effects of the HCG diet can stem from use of the hormone itself or from the extreme calorie restriction that is suggested when using the hormone. Between these two instigators, the side effects can range from mild headaches and fatigue to a medical condition called Ovarian Hyperstimulation Syndrome (OHSS) that affects women.
The hormone HCG (Human Chorionic Gonadotropin) is produced naturally during pregnancy and can be used under medical supervision to encourage fertility in both men and women. The HCG diet claims that self-administering the hormone in conjunction with a severely restrictive diet of only 500 calories (2,100 kj) per day will result in weight loss at a rate of 1 to 3 pounds (2.2 to 6.6 kg) daily. Side effects that stem from hormone use can include head and body aches, lightheadedness or dizziness, and numbness. Swelling and redness or blood clots can also occur.
In addition to these symptoms, side effects of the HCG diet can manifest in the female reproductive system. OHSS causes swelling of the ovaries and can be recognized by the emergence of symptoms such as stomach and abdominal discomfort, weight gain, and swelling of extremities; some cases of OHSS are considered to be life-threatening. Additionally, an increased risk for multiple-birth pregnancies is associated with taking HCG. Since the natural function of the hormone stimulates egg production, women who become pregnant may find themselves carrying more than one child, a potentially harmful event. HCG use during pregnancy or breastfeeding can potentially cause birth or developmental defects.
Side effects of this diet can also be attributed to the extreme restriction of energy, or food intake. Eating 500 calories per day is far below the recommended daily intake for both men and women and may not even be enough energy to support proper brain function. Common side effects of such severe calorie restriction include weakness, irritability, and confusion or disorientation. Long-term calorie restriction can cause wasting of the muscles and organs and lead to heart failure.
Other possible side effects of the HCG diet might manifest as a result of malnutrition caused by calorie restriction. Not eating enough calories to support a well-balanced, healthy diet can lead to deficiencies in vitamins and minerals. Serious medical conditions can result from deprivation of essentials nutrients.