Generally speaking, a drug is substance that is taken to bring about a change in a person’s behaviour or body. Is it biological or chemical??

Chemical.

Explanation:

Drugs are substances that cause an "intoxication". The definitions of an intoxicant are many, but what they all have in common is that they affect the central nervous system by altering the release of various transmitter substances (including serotonin, dopamine, etc.) in the communication between the nerve endings. This will result in more or fewer action potentials in relation to the unaffected state, that is, the communication of the nerves is affected either to be more or less active than usual.

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