Weight-reducing drugs are a far less effective way to lose weight than behavior modification programs involving no drugs, according to a new study.

Four methods of losing weight were tested in the study, which was reported in the July issue of the Archives of General Psychiatry. They were: the common doctor's office treatment of prescribing diet drugs; a course of diet drugs and group therapy; a regimen of drugs and behavior modification treatment; and behavior modification treatment alone.

The common doctor's office treatment was the least effective of the four methods.

The study involved 122 persons, mostly women. The test groups were given the treatments for six months and then monitored for a year by researchers to see which therapy was most effective over the longer term.

In all the regimens that used drugs -- in this case the common precription drug pondimin, which is related to the amphetamines -- dieters lost a lot of weight, rapidly but regained it just as rapidly when the treatment was finished.

"They got used to having the drugs act for them," said Linda Craighead, who carried out the study with Albert Stunkard and Richard O'Brien. "And they relied on it very heavily . . . so when they stopped using it they went back to old habits."

Those who took drugs and went to group therapy lost a mean of 32 pounds during the treatment. But they gained back 20 pounds during the next year.

Those who went to the doctor's office to get a drug prescription and advice on diet and exercise lost only 13 pounds in six months of treatment. These patients were a control group, and their weight was not monitored after treatment.

Dieters who took the drugs and used behavior modification lost 34 pounds initially, but gained back 24 pounds.

Using the drug-free bahavior modification treatment, dieters lost 24 pounds and were still 20 pounds below their initial weight a year and a half after treatment began.

The behavior modification treatment required the dieters to keep diaries of what they ate, and where and when they ate it. After seeing their excesses laid out in time, place, and food patterns, the dieters made contracts with the psychologists to change their habits.

The contracts carried rewards or penalties, thought up by the dieters, for failure or success in changing their habits.

"We used rewards almost exclusively," Craighead said. "They turned out to be simple things such as a quarter put in a jar every day [the dieter] succeeds, or a blouse put on lawaway that she can get if she succeeds. The reward typically doesn't have to be something of great monetary value. Just something to bridge the gap until the social rewards [of being thinner] can take over."