try this site:
http://www.hsa.gov.sg/html/consumer/cda ... ed.html#b4
If your medicines contain any controlled substance listed in Appendix A, you are required to apply for a controlled substance permit from the Centre for Drug Administration (CDA), Health Sciences Authority, Singapore, before your travel to Singapore.
To apply for the permit, please send your written application, at least ten days before your arrival date, by fax or mail to:
Division of Manufacturing and Quality Audit
Centre For Drug Administration
Health Sciences Authority
11 Biopolis Way #11-03 Helios
Singapore 138667
Fax: (65) 64789068, Tel: (65) 68663522
The following documents and information are required to be submitted with your application:
a) Names and dosages of the medicines (both brand names and names of active ingredients contained in the products)
b) Your doctor's letter certifying the medical conditions for which the medicines are prescribed
c) Total quantity of each type of medicines that will be brought into Singapore
d) Your flight details and intended length of stay in Singapore
e) Your address and fax number