I went through the procedure to get controlled substances pre-approved prior to entry to Singapore and it was a totally painless and very efficient process. I completed the application found at this site:
http://www.hsa.gov.sg/publish/hsapor...and_forms.html, sent a very simple letter with the medications listed for my doctor to put on his letterhead, included copies of my itinerary and passport and then emailed the whole thing to the Health Services Authority. Although they request 10 business days advance notice for applications, I received my approval letter within 24-hours. My application was for Ambien and a stimulant for AD/HD and there were no problems obtaining the approval. One thing to note is that prior approval is only required for "controlled substances" which they have listed on their website and other medications only require a doctor's letter or a copy of the prescription.
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