ANNAPOLIS -- The Maryland Senate is making major changes to a medical marijuana bill proposed by Frederick County Sen. David Brinkley. ANNAPOLIS -- The Maryland Senate is making major changes to a medical marijuana bill proposed by Frederick County Sen. David Brinkley.

The Senate is expected to take up final approval of the measure this week, after giving a preliminary OK on Tuesday to the bill and amendments proposed by the Senate Judicial Proceedings Committee.

The bill will now allow people charged with use or possession of marijuana to argue before a judge that they did so out of medical necessity. If a judge agrees, the person would be found not guilty of the charge.

Additionally, the bill proposes a work group to come up with a model program to allow patient access to marijuana by 2013. The program would be through an academic medical research institution and would require further legislation before it could be implemented.

Brinkley said he felt the amended bill makes progress, and it is helpful to people who want to use an affirmative defense for marijuana charges. Under current law, they may use the medical defense and have punishment limited to a fine of less than $100, but would still be found guilty.

He doesn't think the new bill is perfect -- the original version he proposed with Delegate Dan Morhaim, a Baltimore County Democrat, would have established medical marijuana as a controlled dangerous substance and allowed doctors to prescribe it and pharmacies to dispense it.

Under the amended bill, patients "are still going to the black market, so we still don't have any type of legal mechanism for the acquisition of the substance, and that's what the study is supposed to get at," Brinkley said.