A method of sealing parts of a plastic capsule by forming a weld seam in an overlapping region of the parts of the capsule, wherein the capsule comprises a capsule cap having an open end and a capsule body having an open end, and capsules formed by such method. The capsules produced by the process according to the invention are disposable and preferably contain a single dose of a pharmaceutical formulation in the form of a powder or liquid intended to be administered by inhalation and are suitable by their form and function for use in powder inhalers or liquid nebulizers for producing aerosols. Aerosols thus produced can be inhaled, for example, in order to administer a pharmaceutical formulation to the lungs.