Cold and flu medicines containing pseudoephedrine can once again be sold on pharmacy shelves.

The legislation which will allow medicines containing pseudoephedrine to be available over the counter has just passed its third reading in Parliament.

The Misuse of Drugs (Pseudoephedrine) Amendment Bill will reclassify pseudoephedrine from a restricted medicine, allowing the public to purchase it from a pharmacy without a prescription.

Pseudoephedrine is an ingredient used to make the drug methamphetamine - or P - and then-prime minister John Key announced a plan to ban over the counter sales of drugs containing pseudoephedrine in 2009.

The ban came into force two years later with the reclassification of pseudoephedrine as a Class B2 prescription-only drug.

Associate Health Minister and ACT leader David Seymour has been championing his party's policy to return the drugs to pharmacies.

Seymour told Parliament banning pseudoephedrine cough and cold medicines did not end the P epidemic.

"What actually happened is that those people in the business of selling it started to connect with criminal elements offshore and created more sophisticated ways of sourcing P from bigger, badder criminals and managed to bring it in at a lower price and make it more available to P addicts than ever before."

Seymour said it was "incredibly unlikely" that people "are going to return to a less efficient, more expensive way of manufacturing P that involves going around pharmacies and buying up as many tablets as you can".

Due to the state of the health system it was difficult for New Zealanders to get a prescription to obtain these types of medicines and which had "left New Zealanders significantly worse off", he said.

Labour's Ayesha Verrall said her party had supported the bill but had some concerns that she did not feel had been adequately dealt with.

While those seeking meth could seek it more cheaply from overseas suppliers, there will be desperate people who will now have the opportunity to make meth by via cooking it from P, she said.

There were ways to mitigate that, she said.

"I'm particularly disappointed that the proposal that pseudoephedrine be treated like codeine and be required to be kept in a locked safe in pharmacies has not made its way into the bill in its final form."

Verrall said the shortened select committee process meant that some of the potential risks had not been addressed.

Green Party co-leader Chlöe Swarbrick said her party also agreed with the change describing it as moving in the direction of "evidence-based drug law".