Tryptophan is an essential amino acid which we get from our diet, some of which is converted in the body into 5-hydroxytryptophan (5-HTP). Subsequently 5-HTP can be metabolised into serotonin which is a brain chemical (neurotransmitter) known to help control mood and behaviour. Therefore, as 5-HTP dietary supplements help raise serotonin levels in the brain they can have a positive effect on sleep, mood, anxiety, appetite, and pain sensation.
Studies have shown that 5-HTP supplements may be helpful for:
Depression – antidepressant drugs such as Prozac increase levels of serotonin in the brain and as 5-HTP supplements also achieve this it makes sense that they may help to raise mood and may well have fewer side effects than these potent drugs. 5-HTP should not be taken by people who also take antidepressants.
Fibromyalgia - this is a difficult to treat and poorly understood condition. Some small studies suggest that 5-HTP may improve the symptoms which include pain, anxiety, morning stiffness, and fatigue. Many people with fibromyalgia have low levels of serotonin, and doctors often prescribe antidepressants for that reason.
Insomnia - again, there is not a lot of data, but a few studies have found that 5-HTP can help people get to sleep quicker and sleep more deeply.
Obesity - some studies have found that 5-HTP can help with weight loss and many participants in the studies ate fewer calories and felt more full after eating. Given the effect on mood described above, my guess would be that its effect on raising mood may be the reason why it seems to help with weight loss, as we know that people with a depressed mood tend to eat more, often referred to as "comfort eating".
Side effects of 5-HTP are generally mild and may include nausea, heartburn, gas, feelings of fullness, and rumbling sensations in some people.