The potential side effects of increasing serotonin too much include nausea, headaches, anxiety and sexual dysfunction—too much serotonin can interfere with a man’s ability to achieve and maintain an erection, and can inhibit orgasm for both men and women.
This is also true of serotonin reuptake inhibitors such as Prozac.
For me, too much serotonin causes a dull headache.
Side effects are probably much more common when 5-HTP is taken with an SSRI’s such as Prozac.
The body needs to be in balance. Too much of any one chemical, serotonin or whatever, is likely to cause side effects.
Weight Loss Studies Used 500-900 mg per Day
Studies from Italy in the early 1990’s gave between 500 and 900 mg per day to patients to decrease appetite and cause weight loss.
I do not remember these studies mentioning any side effects.
However, Dr. Dennis Padla noted that he gives his patients 100-300 mg, however, patients did not like staying on the 300 mg for long because of side effects, although I did not ask him what the side effect were.
Dr. Padla’s interview is posted here:
Here is the relevant section.
Hobbs: Do you ever vary the dose depending on the response, that is increase the dose if it doesn?t seem to be working?
Padla: Yes. I start with 50 mg per day and increase it to 100 mg, 200 mg or 300 mg if necessary.
Hobbs: What is the smallest dose that you have found effective?
Padla: 50 mg per day.
Hobbs: What is the largest dose that you have found necessary?
Padla: 300 mg, although patients did not like staying on this dose for too long.
Hobbs: Why is that?
Padla: Side effects.
Unfortunately, I did not follow up with a question as to what side effects his patients experience.
The Right Dose
You mentioned that you did not want to take higher doses if 100 mg does the trick.
One of the principles behind pharmacology is to give the smallest dose possible that achieves the desired effect.
I would also be aware of some sites who recommend higher doses in that they may just be trying to sell more product.
I understand the desire to sell more product, but I believe that if you do what is best for the person, sales will be fine.