Diphenhydramine is an antihistamine which is used in the combination with naproxen sodium for the relief of occasional sleeplessness when associated with minor aches and pains. Diphenhydramine has a role nighttime sleep-aid and naproxen sodium is a pain reliever. In addition, diphenhydramine used in relieving symptoms in patients with moderate-to-severe seasonal allergic rhinitis. Diphenhydramine acts as an antagonist of histamine H1 receptor. Besides, was shown potential to repurpose diphenhydramine as an anti-melanoma therapeutic agent, it induces melanoma cell apoptosis by suppressing STAT3/MCL-1 survival signaling pathway.

Bamirastine (previously known as TAK 427), an antiallergic compound that inhibits ligand binding to recombinant human histamine H1 receptor. The drug was involved in phase II clinical trials for the treatment of allergic rhinitis and for patients with atopic dermatitis. However, these studies were discontinued.

Embramine or mebrophenhydramine is an antiallergic agent. Embramine is a histamine H₁-receptor antagonist exerting anticholinergic activity. It may inhibit stimulated platelet functions by inhibiting phospholipase A2. It is prescribed for severe allergic conditions.

Esmirtazapine (S-(+)mirtazapine or ORG-50081) is an enantiomer of mirtazapine (REMERON®), a high-affinity antagonist at 5-HT2/5-HT3 and H1 receptors, used in the treatment of depression. Esmirtazapine has a shorter plasma half-life than the R(−) enantiomer. Esmirtazapine is preferentially metabolized into an 8-hydroxy glucuronide. Organon was developing esmirtazapine for the treatment of hot flushes (vasomotor symptoms) associated with the menopause and insomnia.

Conessine is a plant steroid alkaloid that acts as a potent and specific antagonist of histamine H3 receptors. Conessine displayed high affinity at both rat and human H3 receptors (pKi = 7.61 and 8.27) and generally high selectivity against other sites, including histamine receptors H1, H2, and H4. Conessine was found to efficiently penetrate the CNS and reach very high brain concentrations. Although the very slow CNS clearance and strong binding to adrenergic receptors discouraged focus on conessine itself for further development, its potency and novel steroid-based skeleton motivated further chemical investigation. Modification based on introducing diversity at the 3-nitrogen position generated a new series of H3 antagonists with higher in vitro potency, improved target selectivity, and more favorable drug-like properties. Conessine also has high affinity for the adrenergic receptors. Conessine has being shown to possess anti-malarial activity. In India conessine finds therapeutic use for treatment of dysentery and helminthic disorders.

Bavisant (also known as JNJ-31001074 or BEN-2001), a highly selective, active antagonist of the human H3 receptor that was invented by Johnson & Johnson for the treatment of attention-deficit hyperactivity disorder (ADHD). However, the result of clinical trials did not display significant clinical effectiveness in the treatment of adults with ADHD. BenevolentAI has started phase II clinical trials where investigated bavisant for ameliorating the excessive daytime sleepiness in patients with Parkinson’s disease, using one of the drug side effects is dose-dependent insomnia.

PF-03654746 is a potent, selective antagonist of the human H3 receptor, developed by Pfizer. It was in the clinical trial phase II for the treatment of excessive daytime sleepiness (EDS) associated with narcolepsy, Tourette syndrome as well as potential anti-allergy applications and in phase I of clinical trial for the treatment of Schizophrenia and Alzheimer's disease, but these investigations were discontinued.

PF-03893787 is potent and selective histamine H4 receptor (H4R) antagonist. It has comparable binding affinity to the human histamine H3 receptor. PF-03893787 was found to have significant affinity for the hERG channel. Novartis initiates a phase II extension trial in Atopic dermatitis. Studies exploring the utility of PF-3893787 in patients would be reported in due course, being the potential indications of asthma, pruritus, inflammatory skin diseases and pain, among others.