No – there have been a large number of arrests in our country related to marijuana possession, but in order to accurately evaluate the status of our prison systems, one must look at the convictions, not the arrests. Many drug–related charges are pled down from charges that carry much larger sentencing guidelines and so although they appear as first time drug offences, many of these charges are for “more serious” crimes.
Source: 2000 U.S. Bureau of Justice Statistics, http://www.dfaf.org/whatsright/drugcrime.php