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Weight Loss Drugs: How do they work?

Most Weight Loss drugs either affect fat absorption in the gastrointestinal tract or either appetite or base metabolic rate by influencing the level of certain hormones.

How safe are they?

Currently available weight loss drugs are not safe for long term use and have side effects, some had to be taken off the market because of life threatening side effects.

Are they effective?

Currently available weight loss drugs do not treat the cause of the problem. Hence their effectiveness varies greatly between individuals and do not work at all for some people. Generally their effect is not overwhelming.

Hormones targeted for weight loss

Catecholamines
Adrenalin and Noradrenalin are the catecholamines, which are released as a response to stress. They cause contraction of the peripheral blood vessels, increase the heart rate and increase metabolic rate. Drugs affecting these hormones are very dangerous, especially for people with a heart condition. Side effects are numerous including high blood pressure.

Serotonin
The functions of serotonin are numerous and appear to involve control of appetite, sleep, memory and learning, temperature regulation, mood, behavior (including sexual and hallucinogenic behavior), cardiovascular function, muscle contraction, endocrine regulation, and depression.

Release of serotonin causes a sense of happiness and well being. It is stimulated by ecstasy, nicotine, carbohydrate rich foods. Some weight loss drugs increase serotonin levels to make use of its appetite controlling activity. Side effects include induction of alcoholism and damage of the heart valves.

Human Growth Hormone
Human Growth Hormone production decreases with age and by the age of 80 its levels have diminuished by 90% - 95%. It has a number of different effects; as far as its metabolic role goes they are: Protein metabolism: In general, growth hormone stimulates protein anabolism in many tissues. This effect reflects increased amino acid uptake, increased protein synthesis and decreased oxidation of proteins.

Fat metabolism: Growth hormone enhances the utilization of fat by stimulating triglyceride breakdown and oxidation in fat cells.

Carbohydrate metabolism: Growth hormone is one of a battery of hormones that serves to maintain blood glucose within a normal range. Growth hormone is often said to have anti-insulin activity, because it supresses the abilities of insulin to stimulate uptake of glucose in peripheral tissues and enhance glucose synthesis in the liver. Somewhat paradoxically, administration of growth hormone stimulates insulin secretion, leading to hyperinsulinemia.

Many biotech companies are researching and developing novel weight loss drugs, a number of which are currently in clinical trials. Many of these drugs are trying to use recently discovered hormones which are involved with appetite, the feeling of fullness and detection of body fat levels. It will be some time until any of these drugs become available for use in humans and long term effects remain to be determined.

Some weight loss drugs currently on the market

Drug Brand Name Comments
Dexfenfluramine Redux (withdrawn)
Diethylpropion Tenuate, Dospan affect catecholamine release
Fenfluramine Pondimin affect serotonin reuptake, withdrawn due to high frequency of valvular heart disease
Mazindol Sanorex, Mazanor affect catecholamine release
Orlistat Xenical inhibits fat absorption, incontinence
Phendimetrazine Bontril, Plegine, Prelu-2, X-Trozine  
Phentermine Adipex-P, Fastin, Ionamin, Oby-trim affect catecholamine release
Sibutramine Meridia acts on both the serotonin and catecholamine systems


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