I recently did. Once you get down low enough off on the Zoloft, you can safely start on either or both, but one at a time, of 5-HTP.
I am down to 15mg. of Zoloft and have been on the 5-HTP 25mg. for a few months, doing ok. It is helping to keep my serotoin steady---as with the withdrawal symptoms of weaning off the Zoloft. Many people on the forum have done this successfully.