Both tryptophan and 5-HTP are precursors to serotonin and other neurotransmitters. In fact, tryptophan is a precursor to 5-HTP, which is then turned into serotonin. As a result, it is widely believed that taking 5-HTP as a supplement is a more efficient way of boosting serotonin, as it cuts out one step of the process. This may be the case except for one very important fact: The way tryptophan and 5-HTP interact with the body when ingested are very different, as we shall explain.
When tryptophan is ingested, it goes through the gastrointestinal tract and is absorbed into the bloodstream. It then travels past the blood-brain barrier (BBB) into the brain where it is then turned into 5-HTP, and ultimately converted into serotonin.
Conversely, when 5-HTP is ingested, it too travels through the gastrointestinal tract; but before it is absorbed into the bloodstream, is turned into serotonin in the liver.
The problem with this is that the conversion into serotonin is taking place in the liver and not the brain. The blood-brain barrier does not allow for large quantities of serotonin to be absorbed from the blood. This causes high levels of serotonin to be present in the blood that cannot be efficiently used. What makes dangerous, is that having high levels of serotonin in the blood can cause heart problems, including coronary heart spasms and abnormal palpitations, which cause risk of sudden heart attack. This condition is called serotonin syndrome, and it can be potentially fatal. Whilst this is extremely rare (5-HTP supplements are generally considered safe enough), those with heart conditions or those who take too much will be extremely vulnerable.
For 5-HTP supplements to be effective and safe, they are normally taken in conjunction with drugs that prevent it from being converted into serotonin in the liver.
On the other side, the fact that tryptophan can travel freely through the bloodstream and into the brain before its conversion means that there are is no unnecessary serotonin present within the bloodstream. This makes tryptophan a completely safe choice, and much more efficient in serotonin production.