The US Food and Drug Administration (FDA) has questioned the legality of caffeinated alcoholic beverages and may ban the drinks if producers cannot prove that adding caffeine to alcohol is safe.

The FDA has opened an investigation into caffeinated alcoholic beverages and asked for proof of safety from 30 producers who have products on sale in the US.

"The increasing popularity of consumption of caffeinated alcoholic beverages by college students and reports of potential health and safety issues necessitates that we look seriously at the scientific evidence as soon as possible," said Dr Joshua Sharfstein, principal deputy commissioner of food and drugs at the FDA.

The watchdog has never approved the drinks as GRAS (generally recognised as safe), putting the products in a grey area of the law.

Sharfstein said in an FDA conference call late Friday (13 November) that the group is "not aware of the basis" for manufacturers believing such products are safe and lawful.

Producers notified have 30 days to convince the agency that the drinks are safe, or face having drinks pulled from sale. Sharfstein insisted that the FDA "has not reached a conclusion" either way.

The probe follows a letter sent to the FDA by 19 Attourneys General, as well as other lawmakers and scientists across the US, in which Sharfstein said they expressed "grave concerns" about caffeinated alcoholic drinks.

Following campaigns by the Attourneys General, the two largest brewers in the US - Anheuser-Busch InBev and MillerCoors - have voluntarily agreed to cease production of caffeinated alcoholic drinks. A-B InBev removed caffeine from its Tilt and Bud Extra drinks, while MillerCoors said it would remove caffeine, taurine, guarana and ginseng from its Sparks brand.