Codeine is an opioid analgesic and antitussive medication used to treat mild to moderate pain and relieve coughs. It works by binding to opioid receptors in the brain to decrease the perception of pain and suppressing the cough reflex in the medulla. It is often combined with paracetamol for enhanced pain relief.

Tramadol is a centrally acting synthetic opioid analgesic used to treat moderate to moderately severe pain. It works by binding to mu-opioid receptors in the brain and inhibiting the reuptake of serotonin and norepinephrine, providing a dual mechanism of pain relief. It is often prescribed when non-opioid painkillers are insufficient.

Cetirizine is a widely used, second-generation antihistamine. It is a major metabolite of the first-generation drug hydroxyzine but has been chemically modified to be significantly less able to cross the blood-brain barrier. It is highly effective for the symptomatic treatment of seasonal and perennial allergic rhinitis (hay fever), as well as chronic idiopathic urticaria (hives), providing long-lasting relief from itching, sneezing, and runny nose.

Chlorpheniramine, often recognized in many over-the-counter cold and allergy preparations (commonly known as 'yellow pills' in some regions), is a classic first-generation alkylamine antihistamine. It is primarily utilized for the temporary, symptomatic relief of allergic conditions such as allergic rhinitis (hay fever), urticaria (hives), and the common cold, effectively managing symptoms like sneezing, itchy and watery eyes, and runny nose.