The study did not make clear how many of the addicts were legitimate pain patients who took opioids to relieve their pain or whether they were recreational users who started taking opioids to get high.

Cicero says a crackdown on "pill mills" and doctors overprescribing opioids has made it harder to get the drugs. For those who are addicted, heroin has become the new drug of choice.

"If users can't get a prescription drug, they might take whatever else is there, and if that's heroin, they use heroin," he said.

Heroin is more accessible and cheaper today, said Percy Menzies, president of Assisted Recovery Centers of America, which operates four addiction treatment clinics in the St. Louis area.

“Political events triggered the present heroin problem. 90% of the world's heroin comes from just three countries - Afghanistan, Burma and Mexico. The Afghan and Burmese heroin was a perfect cash crop for insurgency groups and the heroin addiction spread rapidly in countries bordering Afghanistan and Burma. Mexico is a bigger problem for us because farmers in that country have switched to growing the poppy,” said Menzies in an email to Pain News Network.

Opioids aren’t the only “gateway” drug to heroin, according to Menzies. He believes the increasing use of buprenorphine (Suboxone) to treat addiction is fueling the heroin epidemic because addicts have found they can use the drug to ease systems of withdrawal.

“We are seeing more and more patients getting exposed to heroin and it is going to get worse. Sadly, the heroin addiction is being sustained by buprenorphine preparations,” Menzies said.

Menzies has more to say about buprenorphine, marijuana legalization, and "the coming tsunami" in heroin use in this guest column.