Can a landlord forbid smoking?

Yes!

As the owner of private property, you can, and should, ban smoking of any kind. Keep in mind that there are various types of smokables, both legal and illegal. Also, let's remember that individuals who are allergic to smoke/secondhand smoke can worsen some medical conditions.

Consider that legal tobacco is not only consumed via popular cigarettes. There are many leaf tobacco products for pipes and hookahs. Furthermore, some forms of smoke/smoking are part of religious practice. If the case of religious purposes, you will need to consider making adjustments to accommodate this, although it is rare. That last one is not particularly common, but it's something to keep in mind.

When it comes to illegal substances, the matter is cut-and-dry: it is unacceptable and not allowed. We have a clause in our leases banning all illegal substances.

That brings us to the grey area, marijuana. Our advice is to prohibit marijuana completely. Here is what we put in our addendums: "Although in Massachusetts, marijuana is a legal substance, federally, it is still an illegal substance. Cultivating, distributing, and smoking in the unit, yard, basement, attic, or any common areas of this dwelling is prohibited." If there is a tenant with a medical marijuana card, accommodations must be made; however, an owner can still ban smoking, and the tenant will have to use other intake methods of marijuana (i.e. edibles, tincture, oils,) that a property owner cannot restrict.

Ultimately, it is your property and your decision. You can ban smoking indoors and allow it outdoors, in a designated area with ashtray or receptacle for butt disposal. No one wants to see or live in a property littered with unsightly cigarette butts in the yard, driveway, or outdoor space! You can permit certain types of tobacco products while banning illegal substances. The choice is yours, but we always recommend prohibiting smoking of any kind on the entire property. It's our experience that smoking is a turn-off for many potential tenants, especially in multi-family dwellings.