No, gambling is not a sin in itself, however there are things you need to know.
My friend told me it is mortally sinful to purchase lottery tickets or indulge in any form of gambling. Is this true?
No, gambling isn’t in itself sinful, however, there are things that can make it sinful. Here’s what the Church says:
CCC 2413 Games of chance (card games, etc.) or wagers are not in themselves contrary to justice. They become morally unacceptable when they deprive someone of what is necessary to provide for his needs and those of others. The passion for gambling risks becoming an enslavement. Unfair wagers and cheating at games constitute grave matter, unless the damage inflicted is so slight that the one who suffers it cannot reasonably consider it significant.
CCC 2414 The seventh commandment forbids acts or enterprises that for any reason – selfish or ideological, commercial, or totalitarian – lead to the enslavement of human beings, to their being bought, sold and exchanged like merchandise, in disregard for their personal dignity. It is a sin against the dignity of persons and their fundamental rights to reduce them by violence to their productive value or to a source of profit. St. Paul directed a Christian master to treat his Christian slave “no longer as a slave but more than a slave, as a beloved brother, . . . both in the flesh and in the Lord.”
What can make gambling sinful?
As stated above, enslavement to gambling to the point of preventing one from their personal and social responsibilities is a sin, since overusing any morally neutral thing could become sinful when it prevents us from functioning freely and properly as Children of God and members of society.
If the money wagered is meant for something serious, then gambling could become sinful. For instance, using your household feeding allowance for gambling, or school fees or hospital fees. Money to be used for gambling must be something we can do away with, money not needed for any other legitimate obligations.