Ron Crystal, M.D., and colleagues used a disrupted cold virus to which they attached cocaine molecules to create a vaccine that would inhibit cocaine from entering the brains of mice and were largely successful (see Cocaine Vaccination Isn't Science Fiction Anymore).

"We took advantage of the fact that the body has such a robust immune response to the cold virus," Crystal told Psychiatric News.

Others have tested a cocaine vaccine in humans, but used slightly different techniques.

For instance, Thomas Kosten, M.D., and colleagues at Baylor College of Medicine in Houston and Yale University School of Medicine from 2003 to 2005 conducted a clinical trial in which they chemically bonded cocaine molecules to a protein derived from a cholera toxin to form a vaccine, which they used in human subjects.

Specifically, they randomly assigned 58 subjects to receive the cocaine vaccine in five intramuscular injections spaced over 12 weeks, while 57 subjects received a placebo injection on an identical schedule.

On average, all of the study subjects had abused cocaine for 15 years.

Kosten found that vaccinated patients demonstrated varying levels of antibody responses, and only 38 percent of the 55 who completed the entire series of injections produced anti-cocaine antibodies in the quantity (at least 43 mg/mL of blood) that researchers estimated would reliably block drug-induced euphoria.

During the eight weeks of the greatest antibody response, this group provided cocaine-free urine samples 45 percent of the time, as compared with 35 percent for the placebo group and the group with a lesser response to the vaccine.

Of the patients who produced euphoria-blocking antibody levels, 53 percent at least doubled the frequency with which their urine samples showed no cocaine use. Of those who didn't produce high levels of anti-cocaine antibodies, only 23 percent doubled the frequency with which they produced cocaine-free urine samples.

Crystal acknowledged that this research is encouraging, but commented that by bonding cocaine molecules to the cold virus, he hopes to produce a stronger and more consistent immune response in human subjects.