Yes. Clinical psychologists have tested tens of thousands of people worldwide and all humans have been influenced by even small gifts or favours. If someone does you a favour, you feel a sense of obligation—unconsciously, actually—to return the favour.
Doctors were given free samples of drugs by pharmaceutical companies. The doctors didn't use the free samples; they gave them to patients. It doesn't save the doctor anything. It doesn't really do anything for the doctor. Doctors were studied and they all said that those free samples didn't affect how they prescribe drugs at all.
In fact, it affected all of them. It changed their prescribing practices. They started prescribing the drugs that they were given free samples of, even though the free samples didn't do anything for them.