Hope UK made the comments as a Home Office report was released, saying that punishing drug users does not reduce the number of people using them.
The study, which covered several countries, found that drug use had worsened in the Czech Republic since drugs possession was legalised.
Marolin Watson from Hope UK told Premier's News Hour: "It doesn't help people who perhaps were unlucky enough to be caught using drugs once or twice to have a criminal record because that could blight the rest of their lives.
"On the other hand, decriminalising drugs does send out the wrong message to children and young people.
"We don't know how much worse things would be if we didn't have the current system.
"I know that a lot of people argue that it has worked well in Portugal, but they are a different country. Not all countries in Europe have the same problem with alcohol that the UK has.
"After two or three generations of people being accustomed to the use of drugs being acceptable, we may see other drugs becoming as big a problem as alcohol currently is."
The Liberal Democrats and charities such as Release have been campaigning for the decriminalisation of drugs possession.
The Home Office has said it will not change its current stance on drugs in light of the report.