A bittering agent may be applied to therapeuticals to prevent pediatric poisonings, but many drugs inherently taste bitter by themselves.
Bitter taste is thought to have evolved as a way to decrease the risk of ingesting toxic substances, which may explain why many drugs taste bitter. In other words, classes of compounds that may harm the body often taste bitter (Menella et al., 2014). These include the often dangerous compounds like alkaloids and glycosides (source: University of Delhi). These include the familiar psychotropic compounds found in hallucinogenic plants, and the potentially deadly heart glycosides found in Digitalis species, respectively, among other classes of substances.
Paracetamol can be regarded as an alkaloid (Fig. 1), but not aspirin, as it lacks a nitrogen atom (Fig. 2). An alkaloid is defined as
any of a class of naturally occurring organic nitrogen-containing bases. Alkaloids have diverse and important physiological effects on humans and other animals. Well-known alkaloids include morphine, strychnine, quinine, ephedrine, and nicotine...
All of which are quite toxic. As cleverly noted in the comments, aspirin is not an alkaloid in its strictest sense, as it is not naturally occurring. However, it is chemically obtained by acetylation of salicylic acid (Mund et al., 2016), as shown in Fig. 2. Both of the reactants in themselves are naturally occurring; salicylic acid can be sourced from willow bark, and acetylation is a widely occurring biochemical reaction (Gibbs, 2017).
I myself have never had the chance to taste aspirin, unfortunately (although I performed the acetylation shown in Fig. 2 for my Organic Chemistry class :-). Originally, aspirin was developed from salicylic acid (Fig. 3) just because the taste of salicylic acid was so bitter. Acetylation diminished the bitterness, yet the anti-inflammatory action remained (Wu, 2000)). Besides reducing bitterness by chemical modification, masking the bitterness of drugs with, e.g.., sweeteners, can help to overcome the aversion to the bitter taste. This can aid in helping patients, especially pediatric ones, to take their medicine and adhere to their treatment regime (Chauhan, 2017).
Reversely, coming back to your question, adding bitter-tasting additives to drugs indeed seem to be an effective way to reduce pediatric poisonings (Menella et al., 2014)
- Chauhan, J stem cell Bio transplant (2014); 1(2): 12
- Gibbs, Trends Plant Sci (2015); 20(10): 599–601
- Menella et al., Clin Ther. 2013 Aug; 35(8): 1225–1246
- Mund et al., J Occup Med Toxicol (2016); 11: 32
- Wu, Circulation (2000); 102: 2022–3
Fig. 1. Paracetamol, or acetaminophen. source: Wikimedia Commons
Fig. 2. Synthesis of Aspirin, or acetylsalycilic acid, from salicylic acid. source: Imperial College, UK