A new study from the PEW Research Center dives into the 30-year impact of legal penalties for drug-related offenses, and surfaces with yet more evidence to suggest that the way we police, prosecute, and punish drug-related crime has yielded little gain for the American public.

After the rise of crack cocaine in the 1980s and 1990s, Congress created harsher penalties for drug crimes, thereby creating a larger pool of federal prisoners. Nonetheless, the availability, widespread sale and even wider spread use of illegal drugs has sharply increased since over this time period.

“These laws—while playing a role in the nation’s long and ongoing crime decline since the mid-1990s—have not provided taxpayers with a strong public safety return on their investment,” the report concludes.

Meanwhile, taxpayers have been footing an enormous bill. Over the 30-year period, prison spending has increasing almost 600 percent, "from $970 million to more than $6.7 billion in inflation-adjusted dollars."

What’s astonishing about that figure — which has already been studied at some length — is that it goes mostly to punishing lowly, street-level dealers. Nearly half of all those sentenced for drug-related crimes in 2009 were street-level or below.

Moreover, these punished low-level offenders run a broad range of offenses, from large-scale heroin distribution to small-time marijuana hustling. From the report:

“Those sentenced for relatively minor roles represented the biggest share of federal drug offenders. More than a quarter of federal drug offenders—and two-thirds of federal marijuana offenders—were “couriers” or “mules,” the lowest-level trafficking roles on a culpability scale developed by the commission. The average sentences for couriers and mules—defined as those who transport illegal drugs either in a vehicle or on their person—were 39 and 29 months, respectively.”

In short, the penalties haven’t matched the roles for decades, and a huge chunk of that tax bill is going towards locking up your local corner-boys. Just 11 percent of federal drug charges were for high-level traffickers, and yet the average sentence for this offense (101 months) was barely three times that of the average pot dealer. But luckily, PEW notes, federal lawmakers have begun to redress the problem.

The widespread use of drugs — nearly one in ten “admit” to having done illegal drugs in the last month — can be seen in contrast with the falling price of these substances over the last three decades. Even though purity has increased, prices have dropped considerably.

Lastly, and perhaps most aggravating for both advocates and critics of the current war on drugs, is that outcomes for these sentences have barely changed at all. The piece de resistance, here’s what PEW reports in their own words:

Research has found little relationship between the length of prison terms and recidivism rates generally—a pattern that holds among drug offenders at the federal level.

Of the more than 20,000 federal drug offenders who concluded periods of post-release community supervision in 2012 (the latest year for which statistics are available), 29 percent either committed new crimes or violated the conditions of their release. This proportion has changed little since the mid-1980s, when sentences and time served began increasing sharply.

Conversely, targeted reductions in prison terms for certain federal drug offenders have not led to higher recidivism rates. In 2007, the Sentencing Commission retroactively reduced the sentences of thousands of crack cocaine offenders. A follow-up study on the effects of this change found no evidence of increased recidivism among offenders who received sentence reductions compared with those who did not. In 2010, Congress followed the Sentencing Commission’s actions with a broader, statutory reduction in penalties for crack cocaine offenders.