The change would add the two synthetic drugs to a law adopted last year that ended criminal penalties for possession of small quantities of marijuana and cocaine, Colombia Reports said.
Colombia Reports, citing local media, reported Wednesday that some legislators say the synthetic drugs should remain illegal.
Roy Barreras, a member of the Senate and medical doctor, said ecstasy and meth are not comparable to cocaine and marijuana.
"Colombia's problem is in relation to soft drugs, to marijuana and cocaine -- the drug trafficking curse fundamentally depends on these two drugs and world decriminalization will end that business. But mixing decriminalization with these synthetic drugs makes the debate a much more difficult one," Barreras said.
The government has said it will present the plan to the legislature in March.