A number of drugs are capable of changing bodyweight as an adverse effect of 
their therapeutic action. Bodyweight gain is more of a problem than bodyweight 
loss. As bodyweight gain during drug treatment for any kind of disease may be 
the reflection of improvement of the disease itself, we will try to separate 
these effects from those due to drug-induced alterations of the mechanisms 
regulating bodyweight. Bodyweight gain may jeopardise patient compliance to the 
prescribed regimen and it may pose health risks. The body mass index (BMI) is 
determined by dividing bodyweight in kilograms by height in metres squared. A 
BMI of > or = 27 kg/m2 warrants therapeutic action; nutritional counselling and 
programmed physical exercise can be used as a basis. In general, if basic 
therapeutic measures are unsuccessful at controlling bodyweight gain then a 
change of drug might help. Finally, an anoretic drug may serve to support 
dietary measures. However, safety and efficacy has been demonstrated for only a 
few anorectic drugs when used as an adjunct to caloric restriction in the 
treatment of drug-induced obesity. Bodyweight is determined by complex 
mechanisms regulating energy balance. A number of neurotransmitter systems 
acting in several hypothalamic nuclei are pivotal to the regulation of body fat 
stores. Most drugs that are capable of changing bodyweight interfere with these 
neurotransmitter systems. The increment is dependent on the type and dose of the 
drug concerned. Some antidepressant drugs induce bodyweight gain, which may 
amount to 20 kg over several months of treatment. Monoamine oxidase inhibitors 
appear to cause less bodyweight change than tricyclic antidepressants. Selective 
serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors cause bodyweight loss 
instead of bodyweight gain. Lithium may cause large increases in bodyweight. 
Generally speaking, the bodyweight change induced by antipsychotics is more 
often of clinical significance than the bodyweight change associated with the 
use of antidepressants. Again, the changes of bodyweight are dependent upon the 
type and dose of the antipsychotic drug involved. Although almost all 
antipsychotics induce bodyweight gain, molindone and loxapine appear to induce 
bodyweight loss. Anticonvulsants, especially valproic acid (sodium valproate) 
and carbamazepine, induce bodyweight gain in a considerable percentage of 
patients. Treatment with corticosteroids is associated with dose-dependent 
bodyweight gain in many patients. Corticosteroid-induced obesity aggravates 
other corticosteroid-associated health risks. Insulin therapy in diabetic 
patients usually increases bodyweight. Finally, sulphonurea derivatives, 
antineoplastic agents used for the treatment of breast cancer and several drugs 
used in migraine prophylaxis may cause bodyweight gain as well.