In Jainism, gambling (dyūta) is clearly considered a vyasan (vice) and is not acceptable for a follower. It is listed among the sapta vyasan (seven major vices) that a Jain śrāvaka (householder) should avoid, along with things like intoxication, illicit sexual conduct, hunting, etc. These vices are mentioned in texts like Uttarādhyayana Sūtra and later śrāvaka‑ācāra works in both Digambar and Śvetāmbara traditions.

So:

• For the patient – his habit of gambling is against Jain conduct and harmful for his spiritual progress.
• For you as a doctor – treating him is not against Jainism.

In fact, helping a suffering person (physical or mental) is: - An act of dayā (compassion) and ahimsā in practice. - Part of your svadharma (right duty) as a doctor. - Spiritually good, provided your intention is to heal, not to support his vice.

What would be against Jainism is:

• If you encouraged or facilitated his gambling (e.g., treating him so that he can go back to gambling, or joining/benefiting from his vice).
• If you treated him with anger, hatred, or contempt, instead of compassion.

So, from a Jain point of view:

1. Gambling itself is wrong.
2. Treating a gambler with compassion is right and meritorious.
3. If possible, gently encouraging him to leave that vice (without force, with kindness) would align even more with Jain dharma.

If you wish to see more on Jain views about vices like gambling and other vyasan, you can read further here: