There is a growing need for alternatives to hormone replacement therapy (HRT) for hot flashes, especially in at-risk breast cancer or prostate cancer populations where HRT is contraindicated.  L- tryptophan is a precursor to serotonin that, when deficient, can cause a signaling change in the HPA Axis, inducing hot flashes.  Supplementation with l-tryptophan for hot flashes has shown to be effective for some in both research studies and in clinical evaluation. 
 
Reference:
L-Tryptophan as Dietetic Supplement and Treatment for Hot Flashes, Asthenia, and Insomnia in Cancer Patients