Q: Is it harmless to continue smoking?

M: No, tobacco is a poison, it's better to do without it.
Tobacco gives only a temporary stimulation to which there must be a reaction with craving for more. Also, it is not good for meditation practice.

Q: Is there any drug to promote meditation?

M: No, because afterwards the user would be unable to meditate without taking it habitually.

Those who take opium or alcohol are unconsciously seeking the blissful thoughtless state of the real Self. They get an intimation of that bliss by drugs, but afterwards they must resume their normal state and the craving comes back even stronger until they become chronic addicts and slaves to the substance.

With all such artificial stimulants there must be a fall. If the mind is subdued, everything is conquered.