Cannula for dispensing fluid products, particularly for rectal applications, comprising: - at least one tubular body for containing a fluid product to be dispensed which has at least one open axial extremity and a plurality of product dispensing mouths which are provided on the side surface of said tubular body and are split up into at least a first series distributed longitudinally on said tubular body, said tubular body comprising: - a first portion, with a substantially cylindrical shape, and - a second portion, with a substantially truncated-cone shape, which extends from said first portion, - at least one cap fittable substantially to measure around said tubular body to temporarily close said dispensing mouths, - at least one piston fitted axially sliding in said tubular body between an initial packaging configuration and a final dispensing configuration, said piston comprising: - a first section, with a substantially cylindrical shape, that slides inside said first portion of the tubular body, and - a second section, with a substantially truncated-cone shape, which protrudes from said first section and, in the final dispensing configuration, can be placed substantially in line with the inner surface of said second portion of the tubular body, - at least one push rod for actuation of said piston and fittable in said tubular body through said open axial extremity, between said piston and said push rod being interposed temporary mutual fastening means (22, 23), for reversible attachment of the piston to the push rod wherein - in said initial packaging configuration said first section of the piston is fitted in said first portion of the tubular body, - all said dispensing mouths are provided only along said second portion, and - in said final dispensing configuration the outer surface of the second section of the piston is substantially contiguous with the inner surface of the second portion of the tubular body, the shape of said second portion and of said second section allowing obtaining the complete occlusion of all said dispensing mouths once the final complete dispensing configuration has been achieved, so as to prevent any return flows of said product inside said second portion. - at least one tubular body for containing a fluid product to be dispensed which has at least one open axial extremity and a plurality of product dispensing mouths which are provided on the side surface of said tubular body and are split up into at least a first series distributed longitudinally on said tubular body, said tubular body comprising: - a first portion, with a substantially cylindrical shape, and - a second portion, with a substantially truncated-cone shape, which extends from said first portion, - a first portion, with a substantially cylindrical shape, and - a second portion, with a substantially truncated-cone shape, which extends from said first portion, - at least one cap fittable substantially to measure around said tubular body to temporarily close said dispensing mouths, - at least one piston fitted axially sliding in said tubular body between an initial packaging configuration and a final dispensing configuration, said piston comprising: - a first section, with a substantially cylindrical shape, that slides inside said first portion of the tubular body, and - a second section, with a substantially truncated-cone shape, which protrudes from said first section and, in the final dispensing configuration, can be placed substantially in line with the inner surface of said second portion of the tubular body, - a first section, with a substantially cylindrical shape, that slides inside said first portion of the tubular body, and - a second section, with a substantially truncated-cone shape, which protrudes from said first section and, in the final dispensing configuration, can be placed substantially in line with the inner surface of said second portion of the tubular body, - at least one push rod for actuation of said piston and fittable in said tubular body through said open axial extremity, between said piston and said push rod being interposed temporary mutual fastening means (22, 23), for reversible attachment of the piston to the push rod wherein - in said initial packaging configuration said first section of the piston is fitted in said first portion of the tubular body, - all said dispensing mouths are provided only along said second portion, and - in said final dispensing configuration the outer surface of the second section of the piston is substantially contiguous with the inner surface of the second portion of the tubular body, the shape of said second portion and of said second section allowing obtaining the complete occlusion of all said dispensing mouths once the final complete dispensing configuration has been achieved, so as to prevent any return flows of said product inside said second portion. - in said initial packaging configuration said first section of the piston is fitted in said first portion of the tubular body, - all said dispensing mouths are provided only along said second portion, and - in said final dispensing configuration the outer surface of the second section of the piston is substantially contiguous with the inner surface of the second portion of the tubular body, the shape of said second portion and of said second section allowing obtaining the complete occlusion of all said dispensing mouths once the final complete dispensing configuration has been achieved, so as to prevent any return flows of said product inside said second portion.