The sale of inhalants is legal FOR THEIR INTENDED PURPOSES.
However, legality and consequences can also vary from state to state and can be dependent on what the inhalant is.
General info on inhalant use:
"Because products used as inhalants are
legal for their intended purposes, children and teens may mistakenly believe that inhalant use is also legal."
-Source
"Retailers who knowingly sell solvents for this purpose face serious legal consequences."
-Source
State Specific info on inhalant use:
"Massachusetts Law prohibits the possession, use, or sales of any substance for the purpose of producing an intoxicating effect. Punishment for violations includes a maximum fine of two hundred dollars or maximum imprisonment of six months."
-Source
"Twenty-four states specifically ban the use, possession, or sale or other distribution of inhalants. Most define inhalants as products like glue and solvents that can cause mind-altering effects; many specify chemical compounds that, when present in a product, make it an inhalant."
-Source (This source also includes a chart regarding state inhalant laws for all 50 states.)