Many criminal lawyers already say that cannabis bans are nonsense.
"My findings are that political irrationalities in this area are relatively high," said one professor who will be speaking at Monday's discussion in Frankfurt's city hall.
Those testifying include police, economics experts, doctors and drug councillors.
The debate has been "stuck for decades and is ideologically charged," said Green politician and deputy head of city health department Rosemarie Heilg.
Frankfurt is the first German city to officially discuss changing the laws on cannabis consumption.
The morning session will be dedicated to the implications of legalizing the drug. Various models of legalisation will be discussed in the afternoon.
Medical marijuana is already legal in Germany, though it requires a prescription. A court ruling earlier this year paved the way for those with chronic pain to grow their own supply.
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