Jacqui Smith has admitted to smoking cannabis as a student.
The home secretary said she had smoked the drug a few times at university but said she had since steered clear of illegal substances.
The MP, who as a student at Hertford College, Oxford, told the BBC she smoked cannabis "a few times" at university in the 1980s.
"I did break the law.I was wrong.drugs are wrong."
Ms Smith said she had not particularly enjoyed her experiences and pointed out cannabis was weaker during her student days.
The 44-year-old MP denied the admission undermined her position as home secretary.
She told GMTV: "I think in some ways I have learnt my lesson and I have a responsibility as home secretary now to make sure we put in place the laws and the support and information to make sure we carry on bringing cannabis use down, which we are doing.
"On the whole I think people think human beings should do jobs like this. I am not proud about it, I did the wrong thing.
"One of the things about being a politician is that you are often criticised for not knowing what's going on. I hope that my experiences in my life have actually helped me understand that I do want crime tackled."
Gordon Brown announced yesterday the home secretary is to launch a review of drugs policy.
Cannabis was downgraded to a class C drug in 2004 but the prime minister pointed to evidence that stronger strains of the drug are linked to mental health problems.
The Advisory Council on the Misuse of Drugs will review evidence of stronger cannabis and recommend whether it should be reclassified as a Class B drug, putting it on a par with amphetamines.
Ms Smith joins former home secretary Charles Clarke and a number of other ministers in admitting to taking drugs before their political career.
Home office minister Vernon Coaker and public health minister Caroline Flint have admitted to smoking cannabis.
Several members of the Tory shadow Cabinet also admitted to drug taking after Ann Widdecombe called for £100 fines for possession of cannabis in 2000.
David Cameron, however, has persistently refused to confirm allegations he has taken drugs.