The former supreme court justice John Paul Stevens said on Saturday that the federal government should legalise marijuana.

Stevens, 94, was speaking to National Public Radio, in an interview to discuss his new book. Asked if federal law should follow those states – Washington and Colorado – that have legalised the drug, he said: “Yes.”

He continued: “Public opinion has changed and recognised that the distinction between marijuana and alcoholic beverages is really not much of a distinction. There's a general consensus that prohibition against dispensing and selling alcoholic beverages is not worth the cost, and I think really in time that will be the general consensus with this particular drug.

“It's really a very similar problem to the whole problem with prohibition – and of course I lived through that, or part of that period.”

Alaska is due to decide whether it will become the third state to legalise the drug in November.

In his new book, Six Amendments: How and Why We Should Change the Constitution, Stevens also proposes banning capital punishment and limiting gun rights and discusses current controversies over campaign funding and affirmative action.

One of his proposed amendments would change the second amendment, which guarantees the right to bear arms, to say: “the right of the people to keep and bear arms when serving in the militia shall not be infringed”.

Stevens said the only effect of this change would be to remove the final say on gun rights from supreme court justices, and devolve it to individual states, since it is they who define what constitutes the militia in their territory.

Stevens, a leading liberal voice on the supreme court, retired in 2010, at the age of 90. The third-longest serving justice in history, he was appointed by President Gerald Ford in 1975.