I am sorry to tell you that your order can't be canceled because I have already sent out the package.
What you could do after receiving the package is that :
1 - initiate the return order process via the eBay system, and when I get product back, I 'll refund your money back in full amount,
OR
2 - keep the medicine and I'll refund half amount of money that you paid now.
Please let me know your preference and I'll process the refund amount accordingly.