The House of Representatives has rejected a popular initiative to decriminalise marijuana.
A committee had handed in nearly 106,000 signatures in January 2006 to force a nationwide vote on a proposal to legalise the psychoactive drug.
A strong majority of parliamentarians voted against the proposal, with the centre-right arguing that children should be protected.
Supporters of the initiative said that a ban created more problems that it was solving.
The motion is due to go to the Senate for debate, and may yet still come to a nationwide vote.
Switzerland became notorious for its liberal drugs policy in the late 1980s, but public opinion has since changed.
In 2004 parliament threw out a similar proposal put forward by the government, to decriminalise cannabis.
Although the drug is illegal, authorities in many Swiss cantons largely tolerate possession of marijuana in small quantities for personal consumption.