There's nothing more distressing than to discover, after strictly following a diet, that you've not only not lost weight, but you've gained.
One reason this can happen is that some drugs cause weight gain. Most people have heard that insulin and sulfonlyureas can cause weight gain, but there are others as well. It's handy to have a list of such drugs.
So a group of scientists did a literature search and came up 257 randomized trials that included 54 different drugs and weight gain/loss, and concluded that the following drugs have statistically significant effects. Some other drugs seemed to have effects, but either the weight change was not significant or it was supported by what the researchers considered to be very low quality evidence.
Here are the drugs:
**DRUGS CAUSING WEIGHT GAI **
Amitriptyline and mirtazapine (antidepressants)
Olanzapine, quetiapine, and risperidone (antipsychotics)
Gabapentin (anticonvulsant and neuropathy treatment)
Tolbutamide, glimeperide, gliclazide, glyburide, and glipizide (sulfonylureas)
Sitagliptin (DPP-4 antagonist)
**DRUGS CAUSING WEIGHT LOS **
Metformin (suppressor of gluconeogenesis)
and miglitol (starch hydrolysis inhibitors)
Pramlintide (amylin analogue)
Liraglutide and exenatide (GLP-1 receptor agonists)
Zonisamide and topiramate (anticonvulsants)
Bupropion and Fluoxetine (antidepressants)
It's likely that other drugs, especially those similar to these, would have similar effects but no trials of sufficient size have been done to make the effects statistically significant.
It's interesting that most of these drugs (6/10 for weight loss and 8/14 for weight gain) are for treating diabetes. They don't mention insulin.
What this suggests is that control of blood glucose plays a big role in gaining, losing, or maintaining weight. If we can't control with diet and exercise alone, we need to find a drug that will control our BG levels without making us gain weight.
More helpful articles about drugs and diabetes:
Metformin and Kidneys
Drugs and Virtual Patients
Drugs and Supplements