Excipients: Introduction

Last updated: Sunday, December 10, 2023

NB: See learning outcomes for this tutorial mapped to competencies, a PDF of the whole text, and a one-page summary.

☞ Why this subject matters...

Medicines contain one or more pharmacologically active compounds which are responsible for the product’s therapeutic potential. Excipients, or pharmaceutical additives, are all the other parts of the formulation. Although excipients are not the principal 'active' constituents of a medicinal product they do, in many cases, have pharmacological activity. This means they can occasionally cause side effects in their own right. Sometimes an unexpected reaction to a medicine can be explained by considering the potential effects of excipients. Alternatively, a patient or healthcare professional may know about a problem with a specific excipient and ask you to check new medication to ensure that the excipient is not present.

What are excipients for?

Collectively, excipients stabilise a medicine, help with the manufacturing process, aid dispersion of the drug or make the product more appealing to the patient. Two oral formulations are described in detail below, showing you what all the ingredients actually do:

Augmentin 625mg tablets

Sudafed Decongestant Liquid
The body of the tablet contains:

      Co-amoxiclav (the active ingredient)
      Microcrystalline cellulose (used as a binder which holds the tablet together, and as a diluent which bulks up the tablet)
      Maize starch (binder, diluent and disintegrant)
      Silica colloidal anhydrous (improves flow of powder through tabletting machine)
        Magnesium stearate (lubricant in tabletting process)
     Sodium starch glycolate (disintegrant)

The tablet film coat consists of a mixture of:

     Hypromellose (main ingredient of coat)
     Macrogol 4000 (makes the coating more soluble so it dissolves in the stomach)
     Titanium dioxide (white pigment)
     Dimeticone (antifoaming and water-repellent agent and emollient)

The liquid contains:

      Pseudoephedrine (the active ingredient)
      Methyl hydroxybenzoate (E218)(preservative)
      Sodium benzoate (E211) (preservative)
      Sucrose (sweetener and thickener)
      Citric acid monohydrate (lowers pH to where formulation is most stable)
      Glycerol (has multiple uses including as a vehicle, solvent, sweetener and preservative)
      Ponceau 4R (red colorant)
      Purified water (solvent and diluent)

Note that patients may ask to avoid excipients of animal origin for personal or religious reasons. For example, some vegans request medicines that do not contain gelatin, and Jehovah’s Witnesses may seek to avoid products containing albumin from a human source. 

SPS has several reviews on the subject including; 

There is also a review of the implications of cultural and religious beliefs on selecting medicines in Drug & Therapeutics Bulletin Apr 2016 (subscription required).

Excipients and 'E' numbers

Some excipients found in medicines are also used in foods, where they are usually called ‘food additives’. The ‘E’ number system was devised by the EU so that there would be a standard way of identifying additives across Europe. Examples of pharmaceutical excipients that might also occur as food additives include sorbitol (E420), titanium dioxide (E171), sodium benzoate (E211) and tartrazine (E102). If a patient has allergy or intolerance to an 'E' number then you should check to see if it is in any of their medicines. The Food Additives and Ingredients Association provides a comprehensive list of E numbers