HOUMA, La. (AP) — A convicted drug dealer is challenging a state law that requires the purchase of ‘‘drug stamps’’ as a means of paying taxes on controlled substances after being told he owes the Louisiana Department of Revenue more than $47 million.

Todd Matherne, 28, says in a state district court lawsuit that he only learned about the tax when he tried to get a house loan after serving his time following a 2006 guilty plea. It was then that he was told the revenue department had a $47 million tax lien against him.

The 1990 law is one of about 20 drug stamp laws in the nation, according to the Web site of the National Organization for the Reform of Marijuana Laws. Such laws effectively provide opportunities to charge drug dealers for evading taxes and are sometimes called ‘‘Al Capone’’ laws, after the Prohibition-era gangster who was finally tripped up on federal income tax evasion charges and sent to prison.

Matherne was one of three people arrested in Houma in 2005 in connection with a ring that state police said sold steroids and impotence drugs by mail. A state police news release at the time described an operation that sold counterfeit versions of at least seven brand-name drugs. Hundreds of bottles of liquid steroids were confiscated.

Matherne said in his lawsuit that he pleaded guilty to six drug charges and was sentenced to prison but not fined.

‘‘At no time did anyone tell Todd Matherne that he owed forty-seven million dollars to the state of Louisiana when he entered into the plea agreement,’’ the lawsuit, dated March 30, said.

Such a large assessment would effectively deny Matherne any ‘‘any semblance of a normal life,’’ the lawsuit said. It amounts to ‘‘an excessive fine resulting in outlandish debt’’ and ‘‘qualifies as cruel and unusual punishment’’ forbidden by the Constitution.

According to the tax stamp law, each gram of marijuana is taxed at a rate of $3.50. Other drugs are assessed at $200 per gram if sold by weight or $400 per 10 dosage units. Anyone who fails to purchase the stamps can be made to pay twice the amount of tax owed.

Similar laws in other state courts have been challenged with varying degrees of success. Louisiana’s law deals specifically with some of the issues raised in various court challenges. It includes, for instance, provisions designed to protect dealers from self-incrimination by purchasing the stamps.

Figures on how much Louisiana has collected under the drug stamp law were not available when the department was contacted Thursday by The Associated Press. State officials have declined comment on the lawsuit.

The Terrebonne Parish Sheriff’s Office is also a defendant in the suit.

‘‘This is a total frivolous suit,’’ Bill Dodd, the Houma attorney who represents the sheriff’s office told The (Houma) Courier newspaper.