Do you mean the calculation result of you tax return is a positive figure, which is mostly because of the Drug Plan? If so, you still need to pay the amount to Revenu Québec.
I do not know if it is possible to you, but I can pay Revenu Québec by online banking.
Here is the information if you need to contact Revenu Québec:
http://www.revenu.gouv.qc.ca/en/nous_joindre/gatineau.aspx
Please refer to the following sentences from the web site I gave to you:
The Costs – Premium
Generally speaking, persons covered by the public plan must pay a premium, whether or not they purchase prescription drugs. The premium is collected every year by the
ministère du Revenu du Québec when income tax returns are filed. For example, the premium for 2009 will be collected in the spring 2010, when income tax returns for the 2009 taxation year are filed. Persons who pay a premium to the public plan must complete Schedule K of their Québec income tax return.