If by “form” you mean “form of administration” there are two “forms,” intramuscular and intranasal. Intramuscular (IM) is injected via syringe into a large muscle, e.g.,  the butt, thigh, or arm. Intranasal is sprayed up the nose. Both methods of administration are equally effective.
Injectable brands of naloxone are offered by several different companies. Typically, the proper dose must be drawn up from a vial. Usually, it is injected with a needle into muscle, although it also may be administered into a vein or under the skin.
Prepackaged Nasal Spray (generic naloxone, Narcan, Kloxxado) comes in a prefilled, needle-free device that requires no assembly and is sprayed into one nostril while the person lays on their back. This device can also be easier for people without formal training to administer.
The FDA recently approved ZimhiTM, a single-dose, prefilled syringe that can be injected into the muscle (IM) or under the skin i.e., subcutaneously.
For more information about naloxone please see: https://nida.nih.gov/publications/drugfacts/naloxone.
Tacoma Needle Exchange carries both intramuscular (IM) and Nasal Spray (Intranasal) forms of naloxone. We encourage people to carry whichever “form” of naloxone (IM or intranasal) they are comfortable administering.