All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If receiving such gifts would urge the doctor to prefer the drugs produced by the gifting company over others and prescribe them to the patients even though other drugs are better than them, then this is considered an unlawful bribe, which is impermissible.
But if receiving such gifts has no effect on the doctor's work, his sincerity to his patients, and his observation of the rules and etiquettes of his job, then it is permissible in principle.
When it is permissible for the doctor to receive such gifts, it is permissible for others to receive them from him as well, but in cases where it is impermissible for the doctor to receive them, it is impermissible for others to receive them from him.
In all cases, it is safer to avoid receiving or giving such gifts in order to block the means leading to evil.
Allah Knows best.