Dr Brennan is quite right to draw attention to the theoretical possibility that sarcosine might have unrecognised side-effects along the lines he draws attention to. However, it is worth stating that there is no empirical evidence at all that sarcosine does in fact increase risk of prostatic hypertrophy or carcinoma. This possibility could be investigated using animal studies and in the context of properly resourced, large-scale clinical trials. As sarcosine cannot be patented, these would have to be funded by research councils or charitable bodies since no pharmaceutical company is likely to be interested. At present, the evidence strongly suggests that sarcosine is effective in at least some patients with schizophrenia and is well tolerated and probably safe.