Taking 5-HTP supplements has NOT been proven to offer protection.
It HAS been linked to serotonin syndrome - a horrible and possibly fatal condition.
Pre-loading OR taking it with your MDMA may increase the risks.
MDMA inhibits the enzyme (TPH) that is used to synthesize serotonin. It takes a LONG time for the body to reproduce more Tryptophan Hydrolase, so taking 5-HTP is unlikely to make a big difference, especially for heavy users.
It can, however, cause anxiety. This has been reported by myself and others in recovery. I only took 5-HTP a few times before I knew it wasn't any good. I did not just have a shortage of serotonin, I had a shortage of receptors! Shoving more serotonin into my brainstem was NOT what I needed to fix the problem.
Even in non-drug users, HIGH doses of Tryptophan produces anxiety. Taking a lot of it will increase cortisol levels AND cause a prolactin response. Something similar happens with MDMA. You should not expect much euphoria from tryptophan overdosing...
In former heavy users of MDMA, they have found a reduced reaction to high dose Tryptophan compared with non-users. This was after 2.5 years of abstinence. This suggests long-lasting/permanent alterations in the brain pathways that mediate this response.
Drop the 5-HTP. You can get all the tryptophan you need from eating a healthy protein-rich diet in the days leading up to your roll.
Try Piracetam, which has more support among users and may offer protection from toxicity.
Taking a high dose the day of your roll is the most effective, but make sure you allow several hours for the effects to set in before taking MDMA. Take another dose after your roll. This may offer the most protection from the nasty metabolites of MDMA.
Also, try exercising during the days leading up to your roll. Exercise on its own will cause euphoria and will help improve the distribution of neurotransmitters and bloodflow around the brain!